Drill size for M3?

[grandpatzer]

I will drill some hole to mount a external radiator, the radiator uses M3 holes and M3 screws.
So is M3 3mm screw?
Does that mean I should use a 3mm drill bit?

 

[BlacknTan]

It depends on if you want a clearance hole or a hole to be tapped.
If it's a clearance hole, as I suspect, a 3mm drill would be fine.

 

[SEBAR]

I will drill some hole to mount a external radiator, the radiator uses M3 holes and M3 screws.
So is M3 3mm screw?
Does that mean I should use a 3mm drill bit?

It depends on if you want a clearance hole or a hole to be tapped.
If it's a clearance hole, as I suspect, a 3mm drill would be fine.

If you are making a clearance hole for a 3mm screw you should use a 3.5mm bit. If you are tapping a hole for a screw you will need a 2.5mm drill bit and a 3mm x .5 tap.
Here is a conversion chart to inches

Metric Tap Size = M3 x .5
Tap Drill in Inches = #39 (.0995)
Clearance Drill in Inches = 1/8 (.125)​

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[grandpatzer]

It depends on if you want a clearance hole or a hole to be tapped.
If it's a clearance hole, as I suspect, a 3mm drill would be fine.

Indeed it is a clearance hole, I'll use 3mm drill bit

If you are making a clearance hole for a 3mm screw you should use a 3.5mm bit. If you are tapping a hole for a screw you will need a 2.5mm drill bit and a 3mm x .5 tap.
Here is a conversion chart to inches

Metric Tap Size = M3 x .5
Tap Drill in Inches = #39 (.0995)
Clearance Drill in Inches = 1/8 (.125)​

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I would think 3.5mm hole makes the head of the screw aswell go through?
I think I will use 3mm drill, then I do not need to use spacers, as the head of screw will function as a spacer.

 

[SEBAR]

Indeed it is a clearance hole, I'll use 3mm drill bit



I would think 3.5mm hole makes the head of the screw aswell go through?
I think I will use 3mm drill, then I do not need to use spacers, as the head of screw will function as a spacer.

I think the recomended nominal size is 3.7mm. Using a 3mm bit will be to close of a fit. For a close fit you could use 3.4mm.

 

[grandpatzer]

I think the recomended nominal size is 3.7mm. Using a 3mm bit will be to close of a fit. For a close fit you could use 3.4mm.

ah, so the drill needs to be bigger then the screw then?
I'll try 3.4mm, if that is too small I'll use 3.7mm drill bit.

 

[SEBAR]

Indeed it is a clearance hole, I'll use 3mm drill bit



I would think 3.5mm hole makes the head of the screw aswell go through?
I think I will use 3mm drill, then I do not need to use spacers, as the head of screw will function as a spacer.

ah, so the drill needs to be bigger then the screw then?
I'll try 3.4mm, if that is too small I'll use 3.7mm drill bit.

Just use 3.5, it will be perfect. If you are in unsure drill the hole into a scap piece of metal and test fit the screw/bolt first. No sense in redrilling a hole, get it right before you start drilling.

 

[BlacknTan]

A 3mm screw will clear a 3mm hole easily. For one thing, the 3mm screw actually measures slightly less than 3mm over the threads. Secondly, a 3mm drill will always cut slightly larger than 3mm, particularly through sheet metal where the web on the drill will break through before the diameter.
But, if you need more than one hole to line up, location must be very precise, as there's no room for error, so a little extra clearance could be beneficial.
.5mm is .020 inch, and that is a LOT of clearance for such a small hole, at least in my world, but as they say.. to each his own..

 

[Curlyriff]

In the steel beams I am used designing for we drill 18mm holes for 16mm bolts as an example. Divide that for a 3mm bolts and you end up with 3.4mm which is what you need ideally.

This allows for any slight misalignments that you will get within the computer industry as they will not be that precise. We are not using micrometers here (at least not for anything you would personally be drilling out) and you may very well struggle with a 3mm hole not because the bolt wont fit but because you wont get your part you want to align.

I would avoid anything larger than 3.7mm though as you may find slop in the bolt hole instead.

Hope that helps. Kind Regards,

Adam

 

[SEBAR]

I found a good chart listing clearance hole sizes for metric bolts.
http://www.draughtsman.co.uk/information_images/mechanical/clearance_holes.htm

 

[Curlyriff]

Well done Sebar, I was looking for that chart earlier but it's at work.

Kind Regards,

Adam

 

[grandpatzer]

For anyone curious for M3 holes for clearance 3mm bit was perfect.

Most holes the screws went easy in, some of the holes where tight but I was able to either keep drilling with the 3mm bit to make hole bigger or just screw in the screw with help from a screwdriver.