OldTools Archive

Recent Bios FAQ

269788 John Ruth <johnrruth@h...> 2020‑01‑26 Re: Some oldtools finds...MF #2AG anyone?
Bill,

Please get out your magnifying glass, and tell us if it’s really GL1 rather than
G11.

The HSG11 might be intended to be read “HS GL1” where the HS indicates High
Speed [Steel] and the G number is an indicator of Pitch Height on a Ground
Thread tap.  L1 means the Pitch Height is Lower than the standard.

There are GH taps with the Pitch Height Higher than standard and GL taps with
the Pitch Height Lower than standard.

Explained, with a diagram, here:
http://tapmatic.com/tapping_questions_class_of_threads_h_limits.ydev

You might wonder “Why?”  In some cases it has to do with tapping holes in pieces
which are going to be heat-treated.  In some materials, heat treating can cause
permanent dimensional changes, so if you want a standard tapped hole after heat
treat, you must tap the piece with a non-standard tap prior to heat treatment.

Your “AS” tap(s) might be “American Standard,” but don’t ask me how this fits
historically with the USS United States Standard and the NS ( also NC, NF,
National Extra Fine, etc. ) National Standard.

With regard to the 12-20 tap and threads on Stanley planes, look through the
OLDTOOLS archive.  Stanley’s oddball rolled thread is NOT of the “National
Standard” (NS) profile.  IIRC, the peaks and valleys are much more rounded.  I
think the archive has something about hand-fitting threads made with modern
12-20 taps & dies to original Stanley parts.

Every time you buy a package of nuts from one maker and a package of bolts from
another, and they fit, you are standing on the shoulders of giants.

John Ruth,
Who says, “Of threads, and threading systems, there is no end!”

Recent Bios FAQ