Threaded fasteners on cars

[Zeyneb]

Hi there,

How about the following topic. I have two cars and I like to work on them in the DIY car repair shop. When pulling parts I notice various threaded fastener components. You know: Nuts, bolts and washers. Some car assemblies use various types of locking mechanisms. For example for my FWD hatchback I do believe it is very common to mount the front axle to the wheel hub with a castle nut and a cotter pin. This is obviously a secure way to keep the nut in place during a car drive even with strong vibrations. But it is quite inconvenient to use castle nuts everywhere on the car. Another thing is lug/wheel nuts or lug bolts. In the Haynes manual for one of my cars they recommend to apply thread locking compound to prevent the nuts for loosening. But still I believe few people do this and few wheels are flying off. Okay, I’m definitely aware of proper torque and regarding this I do follow manufacturer recommendations carefully. Another example is some shock absorber where the mounting on the rear axle is just done with a flanged bolt and nut, without any wave/split lock washer.

So, my objective is to learn to judge for myself what assembly needs which kind of locking mechanism if any at all. I’ve got some books on mechanical design and a NASA fastener guide (available online) but I wasn’t able to find information on this very topic.

How could I learn more about this topic?

Thanks for your time!

[Stray Electron]

   The first thing that you should probably understand is that there are different "classes" of threads. Automobiles generally use class I threads, the loosest fit, and those are very prone to vibrating loose.  I don't know if it's available in your country but 'Machinery's Handbook' has a huge section on threads. They print a new edition every year so used copies are cheap and widely available and things like threads don't change much.  I probably use my 1938 edition more than my newer editions.

  Unfortunately a lot of the fasteners used on automobiles are odd shapes and it's not easy to find replacements for them so one trick I've started using is to put a small diameter plastic fishing line through the nut or in the threaded hole and the then inserting the male thread. The plastic line makes the nut act like a Nylock lock nut.

  I've never used one but on Ebay and other sites, there are drill rigs that will let you drill diagonally through the corners of regular nuts and then you can use safety wire to secure them.

 FYI  I use anti-seize compound on just about all external nuts and bolts to prevent them from rusting up.  It doesn't seem to make them any more prone to loosening up than untreated threads but does make taking them off much easier.

[T3sl4co1l]

The most important consideration is vibration resistance:
https://www.boltscience.com/pages/vibloose.htm
Shaking the joint in shear, the bolt should not come loose, or faster than some rate.

Some joints are, not only more important than others, but more prone to vibration.  You don't want your wheels falling off, or pistons or engine head -- these get locking mechanisms, like the castle nut, or lockwire, or at least being torqued properly.

Clamping force and torque are important as well, particularly when optimum amounts are needed.  Usually threads are designed for dry fitting, meaning the torque is calibrated for typical friction plus tension divided by the pitch slope (a screw is a ramp in revolution, after all).  Using lubrication drastically reduces the friction and therefore torque required, and may reduce the vibration resistance.

It could well be preferable to go with a dry joint, over lubrication or anti-seize -- indeed rust might be a feature, not a bug.  That last point kinda depends on how often they need to be serviced, how fast corrosion might happen, and if the risk of breaking fasteners is acceptable.  So, lug nuts, kinda eh: there's 4+ of them (usually), so some redundancy there, but subject to vibration and salt spray so they're kind of important; but they might also be serviced every few months/years (depending if you're following a rotation cycle or not ) so might not get too caked up in the mean time.  Other frame components, suspension, control arms, are rarely serviced, but taking more time to do them on the rare occasion they need to, probably isn't a big deal.

Suspension items BTW, are usually mounted in shear, or pinned, so they can be attached surprisingly simply, with just one bolt say, even for something as critical as that.  Well, shear is still the problem, the point, right, but evidently designed in such a way not to be a problem.  For example, they might use relatively large bolts, so the shear slippage is greater than design peak force maybe.  Control arms often have rubber bushings, which helps reduce peak forces, as does the tire itself.

Anyway, I'm just an EE, absolutely there are plenty of resources out there, from handbooks to textbooks.  Lots of hard won experience out there in the ME-sphere, a couple books should do 'ya.  Not... that I know which ones, but, there's a collection of linkages and slides and other mechanisms, that might also be of interest.  Probably one for bolted, riveted and other kinds of fixed joints.  Or, I forget how much of these is covered by Machinery's.

Tim

[tautech]

Generally the manufacturers fastening choice for a specific application is the correct one but like with electronics systems are constantly developing.
The motorsport industry provides the best feedback to manufacturers to develop better systems however as things improve so must our techniques to get the best from new technologies.

Fasteners in themselves wouldn't seem a complex topic however not only the types but the specific application and the metal alloys in use determine what's reliable.

As a kiddy when I first turned spanners thread retaining compounds were still a dream as were most of the high strength alloys each of which uses different fastening techniques for locking, thread size and pitch and fastening torque.
As some example I've worked a lot with magnesium high strength alloys that with the correct fasteners can give strength and fastener torque near to mild steels. 
Yet in the first half of last century locking was often done with wire with bolt heads drilled or castellated nuts and split pins for anything under high stress that in some applications is still used.

However without a workshop manual and significant experience we all at times need guidance for which any of the many thread torque guides can be invaluable and many torque wrenches come with one but there are plenty online discovered with a Gurgle 'thread torque guide pdf' search.

Then of course we need know exactly the tread size, pitch and tensile rating of the fastener we're dealing with so calipers, thread pitch gauges (Metric and Imperial) and sometimes even treading/tapping charts are all required to positively identify some fasteners so to determine their maximum assembly torque.

Then some bolts are single use, that is with correct use they are stretched when tightened to a specific torque but sometimes to a torque then an additional 90^o turn.

No it's not a complex topic at all ! 

[Benta]

I've never in my life seen a wheel fall off a car due to unsecured lugs. Wrong torque, yes.
The fasteners in a car will not work loose if they are torqued correctly (well, perhaps on British cars).
Wheel lugs are no big issue, they generally need 100...120 Nm (unless it's a truck).
For all other fasteners you need the Workshop Manual for the car in question, which will list the torques. In rare cases, threads will need securing, but generally plastering Loctite all over the place is not the solution.

[Jester]

For a daily driver If torqued correctly nothing comes loose. Actual race cars safety wire critical fasteners for example on brakes.

Be aware that using a lubricant like anti-seize when it’s not specified can change the torque applied vs. a dry torqued fastener. Really critical fasteners don’t rely on torque wrenches but instead measure the amount of stretch in the fastener.

I restored / resto-modded a vintage Mustang it was super clean and a pleasure to work on because my hands would barely get dirty working on it. I replaced some of the non stressed fasteners with stainless just so they would never corrode. On the other hand if I check the oil on my daily driver I need to get out the goop to clean up.

[Gyro]

I've never in my life seen a wheel fall off a car due to unsecured lugs. Wrong torque, yes.
The fasteners in a car will not work loose if they are torqued correctly (well, perhaps on British cars).
...

I was once overtaken by one whilst being driven on a highway in South Korea - so I very much doubt that it was from a British car! 

[tautech]

I've never in my life seen a wheel fall off a car due to unsecured lugs. Wrong torque, yes.
The fasteners in a car will not work loose if they are torqued correctly (well, perhaps on British cars).
...

I was once overtaken by one whilst being driven on a highway in South Korea - so I very much doubt that it was from a British car! 

Yet on our Bedford truck pop insisted I was overtightening wheel nuts when using a 1M length of cheater pipe for additional leverage. We nearly came to blows on the matter but instead I decided it was wiser to go and do the following day's work and let him check the wheel nuts for tightness the following evening.
There was damn good reason Bedford went to 10 stud wheels in later model trucks and he never mentioned it again.

Over the years we refined methods of keeping them tight, the dual tires on the rear were the most troublesome but the front would come loose too if undertightened. The original Bedford wheel nut wrench was next to useless for getting them tight enough so not to come loose after a few days use.
Threads clean and oiled were the bare necessity but the nut and rim tapers oiled too allowed real tightness to be applied with much reduced effort but also reduced the cracking force required to undo them.

[bostonman]

I've worked on cars for a very long time. While you want to judge for yourself which types of hardware to use, it really comes down to the project.

One rule of thumb I use when working on a car is to use the same type of hardware; unless you see a reason to upgrade. Also, as someone pointed out, hardware on cars (that I've noticed) seems to be custom sometimes. The last job I did a few months ago resulted in looking on three or four websites along with asking on here, and I couldn't find the same hardware.

The benefit to working on your own stuff (much like electronics): you can afford to spend a few extra on better quality stuff. As an example, I may use higher temperature capacitors, they cost a quarter more or so, but for the extra $1 for four, it's worth it. If you were in manufacturing, well, at a million units, that quarter of a dollar adds quickly.

If you're working on a car and in an area (like the engine) where bolts get very hot, maybe bolts that are decades old are worth replacing; especially if you're doing a job that requires you to dig deep as you don't want a weak bolt to break forcing you to do the job over.

Most bolt heads on cars decades old tend to wear and they are not SAE or metric. This wear eliminates the ability to tighten them properly. At this point you don't have a choice but to replace them. This is when I go on McMaster Carr, start using the filter starting by looking for the obvious. If the bolt is 2" long, I start with that. Then I look at available thread sizes after measuring the one I have to see what they have close enough to offset any measurement error on my part. Sometimes I do enough filtering that I just start over.

As for how to improve quality: If you see a bolt and nut that could use a lock washer, it won't hurt to add one. Sometimes using Loctite is good too, but sometimes overboard.

My personal opinion on some automotive bolts is this: bolts I recently removed on the suspension had a tapered end along with maybe a 1/4" of it not being threaded. I assume these are custom made this way so they are easier to insert into the hole and thread. Most bolts are not tapered at the end, so it takes a bit of tweaking to get the bolt started which adds time if the car is on a production line.

Anyway, for the life of me, I couldn't find these type of bolts. I did find ones that weren't quite as long, but maybe 1/4" shorter (fully threaded). I quickly realized a fully threaded bolt that's a 1/4" of an inch shorter, is the same as a bolt 1/4" longer but missing 1/4" of threads. Although I didn't need to, I added Locktite. Although this reduces the chances of the bolt coming lose, it adds a level of difficultly (especially if it's suspension bolts where they rust and the head loses size) if you want to remove them. Since the suspension work I did will outlast the car, I don't care if the bolts are welded in. In all, it cost me about $50 in replacement bolts, but, the job itself should I have gone to a mechanic would probably be $600. So $60 in parts, $50 in hardware (bolts off McMaster), and I saved along with having a much better set of bolts on the car.

[CatalinaWOW]

While the advice to go to Machinery's Handbook and other mechanical engineering resources is sound, the problem is much more complex than is found in any text or reference that I have ever seen.

In theory, threaded fasteners will not vibrate loose if the tension in the joint is higher than the highest vibration load the joint will ever see.  And this is mostly true, (in fact always true if the conditions of  the theory are met) but the loads can be different than simple theories predict if the mating surfaces are not idea and/or if the vibration vector direction rotates or does some other complex motion.  Most nut and bolt applications utilize this method.  In aerospace it is common to require two methods to assure that fasteners do not come loose.  Torqueing until tension exceeds load is one of the two methods, safety wire, cotter pins, loctite or other method is the other.

The castellated nut with a cotter pin on front wheel bearings is a totally different application.  There is no intent to have any significant preload in the bolt, the intent here is to set a low but not zero pre-load on the bearing.  Without the cotter pin there would be nothing resisting vibration loosening. 

Where we had critical applications that did not lend themselves to measuring tension in the bolt we ran large statistical tests to understand the variability of the relation between applied torque and tension.  Many factors change this, including surface coatings, residual manufacturing coolants and lubes, finger oils, anti-seize compounds, prior installations, debris and dust and I am sure several other factors that I am sure we never discovered.  Note that special thread shapes for locking purposes are available as well as nylocks and other similar concepts also strongly affect this relationship.

In our cases the load required to fix the joint was a large percentage of the ultimate strength of the bolt (already a specialized high strength bolt, far above "Grade 8"), leaving a very narrow window to achieve proper joint operation, allow for the uncontrollable variables and not break the bolt.  In other applications a large bolt can be used, and the window between locking the joint and breaking the bolt is much larger.  This is the case with properly designed wheel lug nuts.  These large margins then allow the joint to succeed and the lug to not fail even when someone decides to lubricate the joint while torqueing it, or pounds on the lug deforming the threads before installation, or just uses an impact wrench and tightens it until it stops moving.

Unless you want to spend a lot of time understanding the loads in each joint in your car, understanding the design concept of the joint and understanding the variables that can occur I would follow the prior advice and just duplicate the car makers original design.  In general they have had many decades to refine their designs, and the errors mentioned for the Bedford trucks are uncommon.

[tautech]

Question for the Yanks.
Why do you call what we all know more correctly a split pin whereas you call it a cotter pin ?
I was taught a cotter pin was tapered and threaded to hold it in position.
Commonly used on the pedal crank of a cycle but also suspension pin locks by some truck manufacturers.

[jpanhalt]

https://www.merriam-webster.com/dictionary/cotter%20pin

Actually, and I have been doing mechanical stuff for more than 70 years, I have always called them cotter pins, not split pins.  Is that why America fought THE war?

[CatalinaWOW]

Just another case of our language being different.  Put in the boot and drive off.

[tautech]

Well looking outside the US a cotter pin is not a split pin.
This is what we might call a cotter pin that is used in truck leaf spring backets and hangers and also found locking steering king pins in place:



It might seem Yanks have yet to correctly name it:
https://www.americanclassic.com/1947-59-Tapered-Lock-Pin/productinfo/74-091/

Yet the Hindus know it like we do:
https://www.indiamart.com/proddetail/king-pin-cotter-20094250655.html


And they call split pins like we do:
https://www.indiamart.com/proddetail/high-quality-split-pin-14136266388.html


Yet if we eBay for 'split pin set assortment' they return Roll pins !   
https://www.ebay.com/itm/165374149361
Seems another misnomer Yanks also call C pins  whereas for decades we've known them only only as Roll pins.

What other funny names do Yanks have for stuff ? 

[bostonman]

BTW, as for learning bolts and stuff while working on cars, I have more input.

I mentioned matching the bolts. Sometimes taking time to learn a single bolt that you removed can teach you quite a bit. People bring bolts and nuts into Home Depot and use the cheat board to find the bolt size and thread. Personally I take time to use calipers to measure length, size, and thread.

The issue I come across is that SAE and metric can be very close which forces me to question whether the bolt is (as an example) 1/2" bolt (as I measured on the calipers) is SAE or a metric 13mm. Also, sometimes counting threads can be like splitting hairs. I may count 27 threads, and wonder if it could be a 26TPI or 28TPI (assuming threads come in this, but I'm just using an example).

This is where McMaster helps. I'll start the filter by bolt type, then bolt length, and then see what thread size options I have. Eventually, before committing to an expensive order, I'll use the cheat board at Home Depot to confirm my measurements. Eventually you'll begin learning standard thread pitch for different bolts.

As mentioned, trying to figure out which bolts to use on a dynamic load can be quite involved. Again, I look for which bolt options I have as I'm not trying to reinvent the wheel. If you work on a car and the bolt is broken due to stress, then maybe you need to buy stronger bolts, but first think about why the bolt broke. Did it break because it's just old, did it break because it seized in the engine head and you snapped it, did it break due to tensile stress, did it loosen because it vibrated and could use Threadlock or a lock washer, etc...?

Often times I also just visualize the dynamic load directions and figure out if a lock washer will do any good, if I should use corrosion resistant bolts because it's under a car where salt and humidity will affect it, and, how long will I be keeping the car. If the original bolts lasted 25yrs and you're replacing them, the car probably won't last another 25yrs, so going overboard isn't worth it; unless it's a restoration and you plan to keep it for many years.

The last job I did on the suspension used bolts that limited options to basically expensive ones. Not that I'd go cheap regardless, but for only needing six bolts, two nuts, and two different size bolts, it cost me $42 (keep in mind in some cases I had to buy a pack of ten when I only needed less than half). I'm uncertain what someone else would have done or where they would have found them (maybe a junk yard), but the bolts were rotted and couldn't be reused. Even if you went to a junk yard, most likely the same bolts are equally rotted and/or how much are you really going to save to buy 25 year old bolts?

One thing people don't realize is the bolts you buy at Home Depot and Lowes are low grade. If you buy a metric bolt, chances are it's 8.8 whereas I would use 10.9 if I can which you can't find at HD. Do I need to use 10.9? Probably not. But for the difference of a few bucks to do a $600 job that will end up costing me just $100 give or take, it's worth it to know the job is done correctly with good hardware.

If you're interested, this is the hardware I used for a suspension job (see below) - they are the McMaster Carr numbers. Thankfully the very large bolts used on the wheels were still good once I cleaned the surface rust. If not, I don't believe they were on McMaster leaving me struggling to find them somewhere else.

One final note: I keep the McMaster Carr app on my phone. If I bring a really odd bolt to the hardware store (and this recently happened to me with a car repair for a bolt that didn't need to be high strength), and it doesn't fit in the M3 or M4 nut on the cheat board, then I have to figure out what it may be. I'll load the McMaster app, look at metric bolts, and then if I see M3.5, it will confirm my suspicions that I'm dealing with a bolt I can't find easy enough in a local store. At that point I've learned an M3.5 bolt exists, whether McMaster has that in the length and bolt head I need, etc... If it comes in the size and length, but not head type, can I change the head type and not cause issues (this is where I'll restart the search by eliminating the filters I selected).

The hardware I ordered is:

93474A239
96595A104
93474A224

[tautech]

Really if you deal with a wide range of threaded fasteners you must have calipers, thread gauges and a drilling tapping thread chart.
The investment is minimal for thread gauges like these:
https://www.ebay.com/itm/114604085277


Drilling and tapping thread charts are all over the net so get those that suit your fancy and needs as none of this is rocket science:
https://mae.ufl.edu/designlab/Lab%20Assignments/EML2322L%20Tap%20Drill%20Chart.pdf
https://trucutnz.com/sites/default/files/ALPHA-TAPPING-CHART.pdf

Add a couple of tensile rating reference charts and you're pretty much all sorted:
https://www.mudgefasteners.com/news/2021/1/24/imperial-fasteners-vs-metric-fasteners
https://www.mudgefasteners.com/news/2021/1/24/deciphering-bolt-head-markings

[CatalinaWOW]

After reading a number of British sources I have concluded we are all using these terms somewhat incorrectly.  A cotter is a wedge or taper used to fix a joint in place.  Probably a pin shaped cotter should be a pin cotter rather that the other way around.  Or maybe a cottering pin.  Split pin should probably be slit pin or bent pin since it isn't split into two pieces.  I have no explanation for the American usage, but note that it seems to be spreading to Britain. 

For fun, think of the removable ball joints used on a wide variety of cars.  A cottered joint is secured by a castellated nut and a cotter pin.  Which may in fact be the source of the American usage.  The pin used to secure a cottered joint.

[Neepa]

Coming from the Aviation side the most used safety variants are either locking nuts with an ovalized neck that presses onto the thread or tab washers if you really want to ensure the bolt or nut doesn't come loose. Other means of locking/securing, at least on the engine sides of things, have largely fallen out of favour.

In recent years safety wire use has decreased due to how time consuming the application of it is and ensuring it is done well.It is also one of the locking types most prone to being neglected due to how annoying doing it is.

You want to make sure the fastener doesn't come loose?
Use single use all metal locking nuts and tab washers. But that gets expensive fast. Although the nuts can be reused if their locking torque is rechecked.
Using these bolts also have a limited lifespan due to the stresses put onto the threads from tightening and loosening them.

General use: locking nuts (all metal)
Really safety sensitive fastener: tab washers

You wouldn't believe how many tons of bolts and nuts are thrown away in modern Aviation. It's cheaper replacing them than the work hour cost of the mechanics.


Just for some general perspective. Aviation is also only cooking with hot water; to use a German expression.

[SeanB]

Yes, which is why I still have a jar of assorted solid rivets, because there was a big box of extra rivets in sheet metal, which was used to make any non critical equipment from, as it saved a lot of time otherwise in sourcing fasteners. Old screws, old nuts and such were in another big series of boxes, mostly sorted by size, and free to use.

[bostonman]

Coming from the Aviation side

I've wondered how many bolts would use wire. If it were enough, added up, it would add quite a bit of weight along with a mess of wires dangling.

Also, is using a flat washer with a split lock washer a good method? I've done research and I never found an exact answer. If just a split lock washer is used, it cuts into both the item being bolted and the nut preventing the nut from turning. If a flat washer is used, the lock washer cuts into the flat washer allowing the flat washer to spin and the nut will become lose.

[Neepa]

Coming from the Aviation side

I've wondered how many bolts would use wire. If it were enough, added up, it would add quite a bit of weight along with a mess of wires dangling.

Also, is using a flat washer with a split lock washer a good method? I've done research and I never found an exact answer. If just a split lock washer is used, it cuts into both the item being bolted and the nut preventing the nut from turning. If a flat washer is used, the lock washer cuts into the flat washer allowing the flat washer to spin and the nut will become lose.

Split lock washers or toothed lock washers are never put directly between a nut and the part itself. They are always sandwiched between the nut and a normal washer. That is to prevent damage to the often quite soft aluminum housings and casings. Damage is to be reduced as much as possible to prevent the slim chance of it leading to further damage to the components from the bite marks.
A real danger would be intercristaline corrosion in the Aluminum itself. The metal simply rots from the inside when that happens.

In older days there were a lot of lockwire secured fasteners. From what I've heard during my apprenticeship there are about 50kg of lockwire on a Panavia Tornado Bomber.

[mzzj]

Coming from the Aviation side

Also, is using a flat washer with a split lock washer a good method? I've done research and I never found an exact answer. If just a split lock washer is used, it cuts into both the item being bolted and the nut preventing the nut from turning. If a flat washer is used, the lock washer cuts into the flat washer allowing the flat washer to spin and the nut will become lose.

AFAIK split lock washers are not much good for anything. Plain nut works better https://www.boltscience.com/pages/helicalspringwashers.htm

NASA fastener design manual puts it out quite bluntly: "its locking ability is nonexistent. In summary,
a lockwasher of this type is useless for locking."

There is better locking washers than split-type but they all scratch and bite in the surface. Wedge-locking washers are supposedly pretty good, Disk-Lock and  Nord-lock are some of the trade names for those.

[tautech]

Well go figure, I'm replacing a cracked head in my SUV and fastener locking methods vary from non-existent, plain flat washer, flat and spring washer, just spring washer and/or maybe with a threadlock.
That's all just in one size fastener which for each application makes perfect sense to me.

[unknownparticle]

Have worked on my own cars and bikes for most of my life, have also helped out in a friends race team workshop for the last 12 years or so.
The worst offenders by far for fasteners loosening off, are British motorcycles!!  Primarily this is because many of them are badly designed, badly made, vibratory heaps of sh1t!! The vibration levels on some of the worst are a danger to health, long term exposure would cause white finger and numb forearms.
This level of vibration is a real problem when spec'ing fasteners, but Brit bike makers just let the customer sort it out for them!  It was exacerbated by using incorrectly designed assemblies that were held together by bolts,  things that compressed the more they were tightened, so could never be held secure. To be fair, many 2 stroke dirt bikes from the 60's, 70's and early 80's were similarly blighted.
Only recurring issue on road cars I've experienced is exhaust manifold bolts, studs, etc. Not surprising really, a bolt or stud that is repeatedly cycled with that degree of heat is asking for trouble unless it is made from a suitable material, which is rare on road cars due to price.
The best way to secure an exhaust manifold is to use clamps, pinching down a flange to the head between the pipes. That way, full exhaust heat is not seen by the bolt or stud.  These are the details to look for when buying a vehicle, it shows care and attention to detail.
Where safety is concerned, like suspension, brakes, etc, manufacturers are more careful, for obvious reasons, so it's veryrare to see problems here.
Race cars are another matter entirely, most people simply cannot comprehend the level of stress that everything is subjected to on race cars, a Porsche race engineer once said, that 1 mile in a race car is the equivalent of at least 1000 miles in a road car!  Problems show up that even surprise seasoned race car engineers. Like for example, unless you have experienced lap after lap of braking from very high speed, like 200 MPH at max braking force, to say 30MPH, it is difficult to understand the stresses involved. So, lock wiring, Loctite, nylocs, aviation spec, and mil spec fasteners will be all over race cars, and every single connection and assembly will have been very carefully thought out.
And the ultimate of course is aviation fasteners, where nothing can be left to chance. So if you want to see the way it should be done, look at an aircraft in detail.  One small bolt can cost $50 easily, and for a reason!

[sokoloff]

I have had the 1987 edition of this book for ages and, if you're interested in the topic, you'll likely enjoy the book as well. I wouldn't say it's a must-have for wrenching on daily drivers, but if you're passionate enough to start a thread on the topic, you'll likely enjoy a couple evenings with it.
https://www.amazon.com/Prepare-Win-Bolts-Professional-Preparation/dp/0615547338

Living in the salty road New England, fasteners loosening when you don't want them to is nowhere near the problem as fasteners not loosening when you do want them do. I'm more likely to need to use a blue wrench (torch) to loosen some crusty old bolt than I am to find something worked loose on a daily driver.

One small bolt can cost $50 easily, and for a reason!

I wish the most expensive bolt was in the $50 range. I've had to have replaced a few sets of triple-digit-each fasteners (and these are airframe, not even in the engine).