.144x37 tpi thread form help

[Lucite]

I've been looking at turning a rear sight leaf spring screw for a 1915 bsa No.1Mk.3* but have had no luck finding the thread form for the .144x37tpi screw. I was wondering if anyone had the thread form or in the least could tell me what the thread angle is.

thanks.

Information

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[Bruce_in_Oz]

It will be "Enfield" Form.

It LOOKS like BA but has a different included form angle.

Then again, Enfield was doing its own thing on a lot of threads.

The thread on the tail of the striker for the No1 Mk111 (and *) reads as:

TPI 30
Angle 56deg 30min


However, the term, "Enfield Form" appears on the dimensions of threaded components shown in the drawings for No1 Mk111 components.

I have a vague recollection that the "included" form angle is 49deg 30 min, but until I can find the actual reference, don't take that as Gospel.

These threads predate the SMLE by some years; they appeared in the Martini Henry series and some of these either came from earlier products like the P-53 or, just as likely, were derived from those of the Swiss and original US (Peabody) predecessors.

And then there was probably a deliberate decision to use threads for which NOBODY outside the Ordnance system had the tooling, not that there was anything like International or even "national" standards at that time. They couldn't even settle on a standard INCH, for goodness sake!

[Lucite]

Thanks for the reply, definitely interesting and from my searches I figured it would be an Enfield thread form. By the sounds of it, it seems that it would be similar to a BA thread angle which I looked it up in my machinery's handbook and it lists the BA thread angle as being 47 degrees 30 minutes. Also In my searches I came across a post on another forum stating that it may also be 49 degrees 40 minutes but that was just reiterating an answer they got from this forum which leads me to believe that 49 degrees x minutes is correct.

[Peter Laidler]

Surely, like most other threads on the No1 rifle, can't you clean out the thread to suit. This was common and approved practice in the UK Military after 1942 with the introduction of the BA threaded No4 and later with the old No series radio sets that had odd mickey mouse sized threads. It's a shame that they didn't apply the same logic with the Bren!

[Bruce_in_Oz]

There must be a few of these "odd" SMLE screws floating about in your neck of the woods.

Try finding old gunsmith shops that did a bit of sporterizing or trade-in. They may have old barrels, complete with springs and screws, tossed in a box out the back. You never know your luck with any of the "Parts" dealers, either.

Failing that, try Alan Hibbs at Kingaroy Firearms here in Oz. Probably cost you more in postage than the price of the screw.

I MAY have a couple out in "the shed" (tm).

[Lucite]

There is one dealer out east that I know of that has them is stock but the cost of postage is a bit ridiculous for such a tiny screw that being said I pulled the one out of my 44' ishapore and if I'm reading the mic right it looks like its 4 BA. I also did the math and assuming all is correct the difference between the .144 x 37tpi and the 4BA is almost negligible so I could in theory turn a screw that's 4BA and with a little gentle persuasion get it to fit with out having to chase the threads.

[Patrick Chadwick]

Check out the dimensions of 6-36. Maybe a trifle loose, but the dodge is to use a mild steel screw (not a hardened machine screw) and deliberately squeeze the threads a touch with side cutters - just enough to provide a bit of friction. Then ease it in.

[Enfieldlock]

Hope this helps:

http://freespace.virgin.net/j.frankl...read-table.htm

[Lucite]

Hope this helps:

http://freespace.virgin.net/j.frankl...read-table.htm

That's actually the very table I was looking at and sadly its lacking a fairly crucial piece of information which is the thread angle on the "enfield form" threads otherwise its very helpful.

[Peter Laidler]

Can't you just follow the officially approved EMER, the bible for real Armourers across the world on this subject and adapt what you have to suit a BA thread. It might not be factory original - whatever that really means - but it will be to an approved military standard. It'd save a lot of faffing around!