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Weight of Threaded Rod
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bostonman:
I have a question about threaded rod.

1/2" stainless steel threaded rod (according to McMaster-Carr) lists 70,000psi. From my understanding, this is the point where the threaded rod will not return to original size after being stretched under a load - and possibly break.

Assuming we de-rate the value by half for safety (35,000psi), how do I know how much weight the rod can take since I only have the psi value?
KrudyZ:
For the rod itself you would use the root (or minor) diameter of the thread to calculate your area.
For a 1/2-13 thread that is 0.417" resulting in an area of 0.136 sq in.
However, you also need to consider what this is threaded into.
Depending on how many threads are engaged and the mating material, the thread may fail (internal or external) and strip instead of the rod breaking.
beanflying:
If it is for a load critical static job then I wouldn't be using threaded rod for a start. You would use 1/2" Bar and turn or cut the threads on the ends and maximise the diameter for the rest of the rod.

Also it matters if the threads are rolled or cut typically a rolled thread will have a slightly reduced diameter than that of a cut thread. So as per the above post you will need to reduce the effective area some more. Typically all thread is rolled for cost reasons.

The other thing is what S/Steel rod are you looking at as it also matters a lot. Stainless Steel consists of a very large range of mechanical, machining and chemical resistance properties. 304 for example is a lot different to say 410.
SparkyFX:

--- Quote from: bostonman on March 11, 2020, 03:26:08 am ---I have a question about threaded rod.

1/2" stainless steel threaded rod (according to McMaster-Carr) lists 70,000psi. From my understanding, this is the point where the threaded rod will not return to original size after being stretched under a load - and possibly break.

Assuming we de-rate the value by half for safety (35,000psi), how do I know how much weight the rod can take since I only have the psi value?

--- End quote ---
PSI = pound per square inch = (smallest) cross sectional area in square inches of the rod x the 70 kpsi = weight in pound before tensile strength limit is reached
Or in other words, a 1 inch diameter rod could hold 70000 pound of (non-moving) weight (given it is attached without compromising diameter, etc. pp). For very long rods the weight of the rod itself needs to be considered.

This is of course all for forces along the axis of the rod, there are other things to consider for sideloading.

As derating happens on the side of the weigth or by upscaling the diameter of the rod, the tensile strength of the material is not affected by it.
bostonman:
Basically I'm going with 3/8" stainless steal threaded rod through five wood shelves to suspend them.

I over estimate each shelf will be 100lbs max, so two rods supporting 500lbs with a nut under each shelf.

Per McMaster-Carr, ss rod is 70,000psi, but I don't know what that means in the amount of weight it can support.
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