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269763 John Ruth <johnrruth@h...> 2020‑01‑24 Re: Some oldtools finds...MF #2AG anyone?
Regarding Bill’s antique tap & die set, Erik wrote:
> I would be unsurprised if there are some uncommon items in that set. I await
the details with great interest.
 
Hmm, Erik! You’ve given me something to think about.  ( I have an inexplicable
fascination with obsolete threads and threading systems. )

Sir Joseph Whitworth published his system of standard threads in 1841.

Our modern U.S. threads began with a paper read before the Franklin Institute in
1864 by William Sellers.

The ASME website states that the use of Sellers threads had become widespread by
the 1880’s.

So, the 1902 founding date for American Tap and Die brings them into the United
States Standard era, which yet mean that it could contain some that aren’t
National Standard or Unified National Standard.  Also, Tap & Die sets tend to
acquire “stowaway” passengers who weren’t in the original set!

Sellers threads include fractional machine threads below 1/4”, sizes most
mechanicians now living have never seen.

[ Collectible open-end wrenches from the USS era may bear strange markings, like
a fraction followed by a hexagon, the fraction being smaller than the actual
measurement of the wrench jaws.  These fit the head of a standard cap screw of
the size shown. ( Shades of British Whitworth practice! ) ]

The numbered sizes once went up to #30 !

You can probably find my tale of being inadvertently sold a New, Old Stock
#14-20 die, in lieu of a 1/4-20, in the archives. That happened circa 1993. The
difference between #14 and 1/4 is only a few thousandths of an inch.

There’s also an older standard for the threads per inch on a 1/2 bolt. The
current UNC Standard is 1/2-13, but older machinery will be found to have 1/2-12
threads.

The “SAE” is a subset of the former standard...the “32nd’s” sizes got dropped.

Yeah, verily, a Tap & Die set from the earliest days of American Tap and Die
could have some pieces that would be very useful to an antique tool collector!

John Ruth
Who, just today, had a chance encounter with a 1-1/4 _triple start_ tap in an
unexpected venue.

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