Motherboard Standoff - Diameter Size

[Rhombuss]

I looked at the formfactors PDF for the motherboard standoff layout here.

If you go to page 13/37, there's a specification pointing to the lower-left mounting hole. It says the mounting hole diameter should be 0.156 inches. Is that even correct? 0.156 inches is 3.96 mm, and that diameter is already larger than the screws you use to mount. Shouldn't the mounting hole be marginally smaller than the mounting screws, so you actually have some material to tap to form the threads?

 

[RPB]

the screws are often 6-32's which have a major dia of .136 of an inch and a head dia of .25 of an inch.

so .156 is the correct size for the hole.

i'm a machinist and i've drilled a lot of holes in the last twenty some years.

 

[fast_eddie]

Full agreement with RPB.
The specs are for the motherboard recommended hole size for a 6-32 screw to pass through; the mobo mounting pan (usually) would need a smaller hole size for tapped threads on a standoff.

 

[Rhombuss]

Oh, I see. I mistook the guide as a representation of the case where the motherboard mounts. I'm working with the metric system, so I've chosen a tapping hole size of 2.5mm - that should be sufficient to tap for a 6-32 screw correct?

 

[fast_eddie]

The correct drill bit for tapping a 6-32 hole would be a #36 (0.106" diameter) whereas a 2.5mm bit works out to 0.098" diameter. IF you are working with a soft material you might be alright; I highly recommend that you get the correct drill bit. 6-32 bits are damn fragile with even the correct size drilled hole, I go thru about 5 or 6 a year due to my impatience to get the job done.

OR

You see about obtaining metric sized standoffs and taps to go with your metric sized drill bits.