Model Forum / General / Models / December 2005

Does anyone know if there's a standard thread for the little brass hex
standoffs as used for computer motherboards etc?

I'm modifying the controls for my CNC mill, and nipped into Maplins
for something to use for mounting several small PCB's. The old Maplins
cat that I keep had a good selection of such things, the new one in
the shop shows virtually nothing. When I asked for 20 of what they
have, I was told their computer showed they have only 10. OK, I'll
take the ten. "Sorry, we haven't really got them, they were sent back
for disposal as we're getting a new range". Of course, they haven't
got the new range in before disposing of the old, that would be too
sensible.
The lad did find me some computer standoffs in a blister pack on the
display racks, but the threads weren't marked and he hadn't a clue
what they were.
The female thread takes a standard M3 screw, but the male thread is
about 3.5mm OD and 28tpi. Difficult to be sure with such a small
sample. I wondered whether it's a hangover from the original IBM PC,
but doesn't seem to match with any of the standard UNC threads, it
would be 6 x 28 which I haven't found listed. Standard M3.5 threads
are much finer, as is 4BA.

I need to tap the backplate to accept these, the nearest tap I have is
5/32 Whit (another oddball) which is too big, but I'll give it a try.

Cheers
Tim

Dutton Dry-Dock
Traditional & Modern canal craft repairs
Vintage diesel engine service