Oli,

 I looked up this box and I see #2 self tapping screws for the PCB, not
32.  Apparently when you went to
 type the tic-tac-toe board for number, you didn't shift the keyboard to
get the upper character.

 With that bit of info out of the way, the #2 refers to the nominal
diameter of the screw.  And of course,
 the 3/16's is the langth of the threaded portion from bwloe the head to
the tip.  The nominal diameter of
 a #2 self tapping screw is .086 inches, which would equate to just
under 2.2mm (.086 x 25.4)

 Regards,

 Jim

> -------- Original Message --------
> Subject: [EE] Obscure screw size
> From: Oli Glaser <oli.glaser@talktalk.net>
> Date: Wed, November 30, 2011 11:18 pm
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
>=20
>=20
> Hi all,
>=20
> I have a Hammond 1551R box into which fits a small PCB.
> The recommended shape of the PCB is given in the datasheet:
> (http://www.hammondmfg.com/pdf/1551R.pdf)
> I have received the PCB and it fits perfectly, but the Hammond box only=20
> came with the 2 screw for the lid and none for the PCB mount holes. The=20
> sizes specified are 2.5mm for the PCB hole diameter, but the screws are=20
> given as 32 x 3/16" self tapping.
> So the question is - what does this translate to in metric sizes? I get=20
> the 3/16" is probably the length, but what does 32 stand for? Is it for=20
> a 1/32" thread?
> I have trawled through pages and pages of all the many different=20
> "standards" - Whitworth, BAS, UTS, etc but I can't fit 32 into anything=20
> that seems to fit properly.
> The UTS (Hammond are US so I assumed this would be the most likely) is=20
> specified as X-Y where X is the diameter and Y is the thread turns per=20
> inch. 1/32 would give a diameter of 0.8mm and 3/16 means nothing in=20
> terms of turns per inch. Even if you swap them round it doesn't make sens=
e.
> Whilst linking to the above datasheet I noticed it's actually different=20
> from the one I have, and gives #2 x 3/16" instead of the aforementioned=20
> 32 x 3/16". This makes more sense as #2 equates to 2.18mm diameter=20
> shank, but I'm still unsure as to the thread (not that it matters too=20
> much as it's self tapping, but I'd like to know anyway)
> I'm going to order some number 2 screws, but can anyone help me to=20
> confirm exactly what the numbers mean for future reference?
>=20
> --=20
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> http://mailman.mit.edu/mailman/listinfo/piclist


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