M4 Mounting hole dimensions

[jtronix]

I just got table where all dimension is mention till M3.5 but i need M4 dimensions.

I know Hole size required for M4 screw
4.152 - For Tight fit
4.445 - For Loose fit

Can anyone know how to to calculate Top Pad size?

[saike]

I just measured a 4mm pan head screw on my bench here. The head diameter is 7.8mm and the flat washer for it is 9.8mm diameter. It is probably a good idea to  get one and measure it yourself, the washer sizes vary a lot.

[jtronix]

I need dimension for create footprint for my PCB.

see attached image which all i need

Note that vias on pad are optional.

mainly i need calculation of D (pad size) like in my first post top pad size is given in chart

[T3sl4co1l]

Pad size depends on fastener head size and if washers are used, their size as well.

We can't answer any more accurately than this.  However, you can peruse catalogs like www.mcmaster.com and find drawings and dimensions for everything under the sun.

Tim

[Siwastaja]

This is not something you can base on a generic table, so please recheck your hole size assumption.

Any M4 screw will always fit into a 4.0mm hole, 100% guaranteed.

So everything you need to do is to guarantee your hole always is at least 4.0mm in size. If you have multiple mounting holes, you need to add worst case dimensional instability and worst case offset error between the holes, so that if one of the holes is slightly at the wrong place, the screws will still fit. Since the PCB manufacturing tolerance, and FR4 stability tends to be very good, the mechanical side dominates: how repeatable are the mounting posts or holes in the case? You'll get this tolerance from the manufacturer of the case, and it will directly determine your hole size - no one can put it in a generic table.

For example, if the case holes are hand-drilled using a template, expect +/-1mm error, necessitating 6mm hole size! If they are hand drilled using a precision jig, the error would be maybe +/- 0.5mm max. If CNC laser cut using modern machinery, then you won't need to worry too much.

For pad size, look at the actual screw you are going to use, and simply look at its drawings; maximum head dimension.

If you don't know the exact screw type you are going to use, or won't have a proper datasheet (i.e., use "generic" hardware store stuff, or Ebay stuff), look up for a few similar looking screws with proper datasheets, use the biggest value you can find, plus add a bit margin.

[madires]

Any M4 screw will always fit into a 4.0mm hole, 100% guaranteed.

Could be a tight fit. Usually 4.2mm work fine.

[mathsquid]

Little Machine Shop has a PDF that gives clearance and tap drill sizes for all the standard small sizes.

https://littlemachineshop.com/images/gallery/PDF/TapDrillSizes.pdf