17-12-2019, 02:16 PM
(This post was last modified: 17-12-2019, 02:26 PM by Ian McGowan.)
I am no expert Jon but, I believe that 3/8" x 26TPI is a British Cycle thread (60 degree thread form) see here
http://www.oldengine.org/members/diesel/...cycle1.htm
I also believe that 1/2" x26TPI is a Model Engineers Standard thread (Whitworth form) see here.
http://www.oldengine.org/members/diesel/Tables/me1.htm
Equally, both could be Brass Pipe Screw threads, (whitworth form, 55 degree thread angle. All British Pipe screw threads from 1/8" to 1-1/2" are 26 TPI. see here.
http://www.oldengine.org/members/diesel/...brass1.htm
I can only suggest that you find someone with a comprehensive set of thread gauges and who knows how to use them.
http://www.oldengine.org/members/diesel/...cycle1.htm
I also believe that 1/2" x26TPI is a Model Engineers Standard thread (Whitworth form) see here.
http://www.oldengine.org/members/diesel/Tables/me1.htm
Equally, both could be Brass Pipe Screw threads, (whitworth form, 55 degree thread angle. All British Pipe screw threads from 1/8" to 1-1/2" are 26 TPI. see here.
http://www.oldengine.org/members/diesel/...brass1.htm
I can only suggest that you find someone with a comprehensive set of thread gauges and who knows how to use them.