An unusual thread size?

I have bought an old Stanley 78 rebate plane. These tools pretty much always lack either the rebate width or depth stop when sold on the second-hand market - in my case it's the depth stop.

I can machine a new stop OK but I'm foxed by the thread on the screw which attaches it to the body of the plane. The screw from the width fence fits, and measuring from that it seems to be 3/16" x 28 TPI - which doesn't seem to conform to any standard. Tracy Tools list dies for this size (no stock, and anyway I'm not going to pay £24 for a one-off) so it must be a 'thing'.

Push comes to shove I could machine the thread, but would prefer to buy something ready made if possible.

Any advice?

Robin.

Edited By Robin Graham on 01/12/2021 01:06:04

I don't know about unusual thread size; this is certainly an unusual thread in that a Robin Graham asked practically this same question yesterday under "General Questions", where it received several interesting and helpful replies.

Is there, improbably, more than one Robin Graham with a Stanley 78 rebate plane on our forum, or is our one Robin Graham experiencing a version of Groundhog Day?

If you use your favourite search engine on "Stanley Plane Thread Sizes", there is a wealth of information, all concurring that it's a current non-standard size, some say 3/16"x28, others No.10x28, neither of which help you, because it's no longer a standard, if indeed it ever was one.

Easiest solution to me is to buy an M6 thumbscrew off eBay or similar, and turn off the thread, almost all the way to the top. The remaining bit will allow a nut to be Loctited on and turned down to form a collar.
The rest, when the thread has been turned off, is almost spot on size to cut a 28tpi thread.

(or, as mentioned previously, the thumbscrew on mine is a rattling good fit, so you might just get away with an undersized 1BA @ 28.3tpi)

When you've got those sussed, try Singer sewing Machine threads next, where you will find several 3/16"x28  were used..
https://www.singersewinginfo.co.uk/screw_threads

Bill

Edited By peak4 on 01/12/2021 02:02:11