I've two pre- WW1 threads one measures at 6.3mm across the threads and is
I don't know why the two different threads have been used, one is a stud and one a bolt in the same casting doing the a similar job (one is holding down the cylinder end plates the other the steamchest cover)
Steve
In message , Steve W writes
1/4" x 20TPI is BSW 5/16" x 18TPI is BSW
If nothing else, it would prevent stud and bolt being interchanged.
Except 5/16" is nowhere near 6.7mm.
Thanks for the link to the miniature threads page. The story on parsing sharp edged irregular holes is a new one to me:
Absolutely fascinating, thank you. The parser looks potentially useful, maybe one day I'll need to try it.
David
Assuming you really do mean 6.7mm (not 6.3mm ?) it must be 17/64 x 18 tpi ? Which would make it easily the oddest thread I've ever heard of. I've got a couple of 1/4 x 18 tpi threads to cut for some replacement parts for a telescope mount - the originals use that thread in preference to 1/4 x 20 tpi for no reason I can fathom.
Have a look at 5/16"
First one is 1/4 whit. Second one is 17/64" x 18 OK so it's special but you asked what it was. No metric is close either in diameter or pitch.
17/64 was a 'standard' at one time in the cycle threads.-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:-
16-18 ASME would be 6.807 mm dia and 18 tpi
Which is almost as helpful for single pointing it on a lathe!
Mark Rand RTFM
Bear in mind these are pre-WW1 and probably handcut. They are corroded making good measurement difficult, esp thread angles
Thanks John, you are probably on the money as the workshop the engine was made in did manufacture bicycles from scratch at the time the engine was built.
Steve
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