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RE: Screw sizes

To: <triumphs@autox.team.net>
Subject: RE: Screw sizes
From: "Randall Young" <ryoung@navcomtech.com>
Date: Tue, 12 Feb 2002 22:28:32 -0800 o m>
> When they say a screw size is 10-32UNF what do they mean?  I think the unf
> is for universal fine right?  What would a 3/16" dia screw be?

UNF is just one of many thread systems running around, it stands for Unified
National Fine.  I'm sure someone will correct me if I'm wrong, but I believe
the UNF and UNC thread systems do not use fractional sizes below 1/4", but
rather 'screw sizes' like #10.  However, 10-32 (and it's UNC mate 10-24) is
pretty doggone close to 3/16".  3/16" is .185", my thread chart gives the
major diameter of #10 as .190".  However, 'major diameter' is a theoretical
number, you'll get a smaller value if you just put some calipers on an
actual bolt.  So, a 10-32 will measure pretty close to 3/16".

According to the thread chart I have, an actual 3/16" would be either BSW
(3/16-24) or BSF (3/16-32).  But I believe the NS (National Special) system
lists fractional sizes down to 1/16".  ISTR the old SAE system did too, but
I don't have a reference handy for it.

See for example
http://www.fullermetric.com/Dimensional%20Information/PDF%20Files%20Technica
l%20Information/Thread%20Identifications%20Chart.pdf
or, go to
http://www.fullermetric.com
and click on 'Technical Info' at the top of the page.

Randall

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