Identifying a Parker Hale thread size.

I am modifying a Parker Hale back.sight to take modern eyepieces, The thread size is giving me some hassle as far as identification is concerned.

The diameter of the thread is 0.249" and the pitch is an excellent match to my 0 BA thread gauge..Unfortunately the diameter of an 0 BA thread should be 0.236" and indeed an 0 BA screw is a rattle fit in the threaded aperture.

I have some comprehensive books on screw threads, but I can't find anything that matches. Just wondering if Parker Hale had their own standards or is there a series of gunsmith threads that I am not aware of?

Andrew.

Edited By Andrew Tinsley on 19/04/2021 11:26:04

0.249” might be a worn, or deliberately truncated, M6

Have you checked the angle, or only the pitch ?

MichaelG.

0 BA is cited as .236" dia x 25.4 so maybe you have a 1/4" x 26 TPI thread. M6 dia is also .236" so it won't be that.

Tony

Edited By Tony Pratt 1 on 19/04/2021 11:32:00

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Oops ... my error, Tony

I was concentrating on the thread form and shouldn’t have mentioned diameters.

MichaelG.

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Edit: the defining question will probably be ... what is meant by “an excellent match” ?

Edited By Michael Gilligan on 19/04/2021 11:42:46

Hello Michael,

The sight is from the early 1950's I would be amazed that Parker Hale would use a metric thread. But stranger things have happened! I have checked for 25 and 26 tpi and the thread is definitely between those limits. It seems to be a pretty definite 0 BA pitch. It is very difficult to see if the thread angle is 47.5 degrees. However an 0 BA thread gauge seems to block out virtually all the light so I suspect the angle is closer to 47.5 than 55. I have run out of bulbs for my shadow graph so I am stuck for a better means of measurement, until I order up some replacements.

I will check for an M6 size, it certainly isn't a worn thread, as I doubt it has ever been unscrewed since it was made (no reason to do so). If it is M6 then it has been truncated. The crests appear bright and the rest is black, so it could be so,

Andrew.

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Don’t bother with the ‘truncated M6’ hypothesis, Andrew ... that was a silly slip on my part.

MichaelG.

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Any chance you could post a close-up photo of the male thread ?

Edited By Michael Gilligan on 19/04/2021 11:53:18

Hello Tony,

Interesting suggestion for a 26 tpi x 0.25" cycle thread. The threaded depth is only 0.2" so the slight mismatch in tpi would not matter, better than a rattle fit 0 BA. Cycle thread is 60 degree and my eyesight tells me that the thread angle is less than this (may well be wrong!)

For all practical purposes I think that a 26tpi x 0.25 thread is likely to be the nearest to what I have. Advancing years an eyesight doesn't want to get involved in screwcutting in small sizes, so I will get a 26 tpi x 1/4" screw and see if it is close enough!

Andrew,

P.S. Hold on why am I talking British cycle thread, when a 1/4" BSF thread will do the job!

Andrew

Just a thought British Brass thread 1/4" is 26 tpi x 55 deg may suit better than cycle 60 deg thread

Jonathan

Hello everyone,

I just tried a 1/4" BSF screw and although a touch loose, it will be good enough for what need to do. Effectively I want to make a male to female adapter bush to go from the old Parker Hale male thread to a 9.5 x 1.0 mm female thread.The bush needs a hole through it, otherwise you can't see the target!

I shall threadlock the 1/4 BSF thread into the sight body, so the slightly slack fit will not be a problem. Still curious as to what the thread is, but getting the job done is more important.

Thanks everyone for your help and suggestions.

Andrew.

Funny this should come up , I know nothing about shooting but was given a .22 Parker Hale Dragon a few months ago and keeping meaning to buy a scope for it !

Gun-makers were once notorious for doing their own thing with threads, so it might be a special. Otherwise, spoilt for choice, because just about every system in the world has fasteners close to 1/4", and with similar pitches. Helpful to establish the thread angle to narrow it down.

BSF ¼" = 26tpi, 55°

BSW ¼" = 20tpi, 55°

BA0 = 25.4tpi 47.5°

BSB ¼" = 26tpi, 55°

BSC ¼" = 20 or 26tpi, 60°

UN ¼" = 20, 28 or 32tpi, 60°

Or M6x1.0 = 25.4tpi 60°

As the largest market for guns and accessories in the 1950s was the USA, it might be a National thread, which are similar to the UN series.

Hateful how small details can cause big problems! I suppose it's all part of the fun...

Dave

It would not surprise me in the slightest if Parker Hale put a BA thread form on ‘skimmed’ 1/4”

MichaelG.

Parker Hale threads are bastard size and form, i cannot be any more helpful than that I'm afraid.

Robert Butler

There was an eaarlier post on Parker-Hale threads which may help.

https://www.model-engineer.co.uk/forums/postings.asp?th=28226

Brian

My memory may be faulty, but many years ago when I bought an iris aperture for my Gamo 126, the man at Fultons of Bisley had a choice of 1/4 BSF for P H and 8mm, I had the 8mm.

Hi all, Parker Hale sometimes iused BA,which is metric equivalent, look in Machinery Handbook for alldetails, and also they used UNF,UNEF , and number un sizes, good fun eh,

PS i am a gunsmith