Mounting PCBs in Rack Enclosure

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How do you mount PCBs to the bottom (or top) of a rack enclosure without anything like a pan head sticking out?

In commercial gear there are usually depressions in the sheet metal to account for a screw head. Is there a hand tool that can do this sort of thing?

I've got a nice Hammond 1U RMC enclosure but there is absolutely no room for screw heads above or below. I am at a total loss as to how to actually mount anything to this enclosure.
 
You can use a flat head screw, and countersink the hole so it sits flush. The little plastic snap posts can have a very low profile as well. Pop rivets have a low profile, you could use them to mount some sort of internal brackets.
 
Yeah, I think the coutersink method is just about the best method at this point.

I can't believe there's not a better way to do this. After searching the WWW I am really NOT impressed with sticky tape'd plastic standoffs and other such hackery.

The standard male-female standoffs are not quite right:

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Anyone know of a 6-32 0.25" / 6.35mm hex standoff with a shorter male end like only 3mm long?
 
I found male-female M3 5+4mm standoffs. And the 0.5mm pitch thread would mean up to 4 threads would grip 2mm sheet metal whereas with 6-32 only 2.5 threads would grip. With a washer these standoffs might not stick through more than 1mm or so. If the hole were just right, brass into aluminum might not even need tapping.

But I suppose the countersunk screw method is probably still a little better. But with these parts:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


The two screw ends might butt into one another leaving about 0.087" slack by my calculations. Unfortunately I have found that 1U enclosures can be very tight with things like radial capacitors (especially filter capacitors of power supplies). Maybe a washer could take up the slack.

The square rod idea is interesting. If the intention is to lay down a long square rod extending beyond the ends of the PCB, that would also solve the butting threads problem with standoffs. The only problem is that I do not have the tools to accurately drill 0.25" square rod.
 
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