Lee Enfield No. 1 Mk III striker screw pitch

[sp00ky2]

Does anyone know what the thread size is for the screw that captures the firing pin on the back of the cocking knob of a Lee Enfield No. 1 Mk III?
I had to drill this out and would like to run a tap through to clean it up.

http://www.marstar.ca/dynamic/product.jsp?productid=78400"]Marstar Canada - Striker Screw (LEE-053)

Information

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[Alan de Enfield]

Screw, Striker, Retaining = 0.144 dia x 37 tpi

It is what is known as an Enfield Thread, unlikely that you will find any taps / dies for these threads.

[sp00ky2]

Thanks for that Alan.
I tried an 8x36 tap as it looks as close as I can get, but no go.

[Bruce_in_Oz]

EVERY thread on a No1 (SMLE) is either an "Enfield" or "trade" special.

It's not just the pitch or diameter: Enfield had their own ideas about the form of the thread. Even the stock bolt, whilst VERY close to a 7/16" 14TPI Whitworth, has a "special" thread form.

The stock bolt for a No4 is essentially the same as for a SMLE.

The breech threads on SMLEs and No4s have the same pitch and the same nominal diameter. There it ends; No4s are Whitworth form, SMLEs are VERY Enfield.

However, EVERY other threaded fastener on a No4 is either BA, BSF or BSW. This actually helped immensely in the rapid buildup of wartime production; there were thousands of small and large engineering "shops" that already had the tooling to make screws. In WW1, a lot of effort was expended in supplying the special tools and gauges to make the same items for SMLEs.

The Mk6 / trials No4 were built using mostly the old SMLE thread system, hence all of the drama about keeping them separate from "real" No4s when things got lively.

P-14s are full of "Enfield specials" as well. That must have been fun for the American manufacturers who were well on their way to their own "unified" thread system. It was the automotive industry / SAE that drove the standardisation case very hard.

From a logistics / armourer's perspective, all of these odd threads are (up to a point), a blessing in disguise. Only "proper" fasteners will fit and work as prescribed. Thus, there is somewhat less likelihood of some enterprising digger replacing a missing screw with some pierce of crap from the local bargain store.

[Peter Laidler]

In our last EMER's for the No1 rifles still in service, dated in the late 50's or early 60's as I recall, there was a list of screws/threads in the No4 rifles that could be adapted from standardised BSF's/UNF's/BA's by cleaning out with a tap or die. But I don't seem to remember the screw striker being there.

If the screw thread in yours is totally sha........, er..........., knackered spooky, tyhen you could use a No4 striker and cocking piece as they interchange as a set

[breakeyp]

And to stir the pot with additional useless information, US manufactured arms from flintlocks to the end of the trapdoor Springfield .45-70 use French developed thread sizes. The US bought tooling from the French for the Charlieville (sp) flintlock and things progressed from there. The older Dixie Gun Works catalogs had two pages on Turner Kirkland's investigations into this interesting area the arcane.

[Bruce_in_Oz]

As the old saying goes:

"That's the great thing about "standards"; there are so many to choose from!"

[Patrick Chadwick]

Screw, Striker, Retaining = 0.144 dia x 37 tpi

It is what is known as an Enfield Thread, unlikely that you will find any taps / dies for these threads.

4BA is close. 0.142 dia x 38.5 tpi. Since the thread is sharper, 4BA will probably work quite well to clean up a striker screw thread, which is only about 1/4" long. Just use "two finger" torque, no wheel-brace stuff!

If you are unfortunate enough not to have BA equipment, then 6x36 would be next best. 8x36 is far too thick!

[Peter Laidler]

Now you mention it Patrick, I seem to remember that the 4BA was used to clear out the No1 rifle sling swivel screw holes to enable No4's to be used.

[Bruce_in_Oz]

That bit of "creative" engineering; using a BA screw to replace the sling swivel screws continued in Oz until the last SMLE snipers and No2 .22 trainers went out of service.

The screws are SUPPOSED to be staked into final position. In order NOT to destroy the thread in the outer band, the "staking" had to be carefully removed using a suitable drill-bit. Notice that the proper screw has a small "cup" on the threaded end. This is to guide and steady the centre-punch as it is being whacked with a large hammer. It also provides the alignment for the drill-bit used to cut away the flared end. Failure to remove the resulting flared out end of the screw before removal will result in a destroyed band.

EVERY time a rifle was given a proper inspection or detailed examination by an armourer, that little screw was removed so that the furniture could be removed. It was also a requirement that the replacement screw be staked in position.

As near as I can discover, it was the ONLY screw that got this treatment and thus was consumed in fairly large numbers on an annual basis.

Several other screws are to be staked, but usually by spiking component metal into the end of the driving slot.

These days we have LOCTITE.