Screw Threads

May 18th, 2011,

I happened to be reading about the history of screw threads (just to give you an idea of just how exciting my life is!) and thought the information interesting and may even have application to our understanding instrument manufacturing.

The first attempt at screw thread standardization was in 1868 with the USS (United States Standard) for coarse threads.

The SAE (Society of Automotive Engineers) standards were adopted in 1911. The SAE included finer threads.

The American National Screw Thread Standard was adopted in 1924 and included classes of Loose Fit, Free Fit, Medium Fit and Close Fit. And two series were defined: Coarse, and fine - which roughly followed the USS and SAE standards.

The standards were further refined in 1935, adding an extra fine series.

And, in 1949 the Unified and American National Screw Thread Standards were adopted with six classes of fit.

In Europe, metric measures were used but there was no standardization between countries until 1948. with the ISO (International Standards Organization). with three series of threads.


Reply #1 - May 20th, 2011,

You forgot to include the Acme square shoulder, the radius apex threads, and the British Whitworth threads, plus many unique specialty threads.


Reply #2 - May 20th, 2011,

You're right. I did skip over Whitworth, which dates to 1841 as a standard in Britain. It became the British Standard Whitworth Thread, but I never found a date for BSW, just "later". It was a coarse thread. There is a BSF standard as well, but I didn't find a date on it.



Acme threads or a modified square thread had an old standard and a new standard that came out in 1952.

I didn't find anything on radius apex threads.

Some of those standards would probably have never found their way into the manufacture of instruments, except maybe as tools.


Reply #3 - Jul 2nd, 2011,

British Standard Whitworth and British Standard Fine B.S.84:1956.


Reply #4 - Aug 30th, 2023,

Resurrecting an ancient thread to point out that non-standard screws persisted will into the 20th century in some industries. Singer sewing machines are known to have made most of their screws in-house that match no known standard.


Reply #5 - Aug 31st, 2023,

In the case of the earlier threads, I suppose they existed simply because there was just a burgeoning notion that standardization might be labor saving.

But, for industries that continued to use an off standard thread late into the 20th Century, the only explanation I can only think of is that it would force users keep coming back to them for parts and service.

There may be other explanations, that haven't occurred to me.


Reply #6 - Sep 2nd, 2023,

Proprietary threads certainly would have necessitated buying them from the OEM - but another possible explanation presents itself, at least in terms of Singer Sewing Machines: They had been making these screws since before there really were any recognized standards - some of their models were made for many decades - changing would have created a logistical nightmare. Plus the equipment and fixturing were all bought and paid for. Even changing on a new model would be somewhat of a headache - a presser foot screw was a presser foot screw, etc, etc. *shrug*