Thread identification

I have been tasked to make some small screws. I have been given a sample to work from. The thread appears to be 48 TPI with an outside diameter across the thread major diameter being 4.54 mm or 0.1785 inches. I cannot see a thread of these dimensions could anybody suggest what it could be.

sometimes it can help if we know the purpose of the screws or the equipment they are intended for and manufacturing country of the equipment.

Hi Peter,

Have you any idea what the screws are used in or country of manufacture of the assembly?

Tony

This site has a good selection of thread tables including some very obscure ones:

http://ac2litre.com/fasteners.html

Russell

My guess is M4.5 x 0.5 (from the metric fine series)

Possibly 4.5 mm metric fine which has a pitch of 0.5 mm (Which is 50.8 TPI.)

If you have a screw and nut you could measure how far the nut moved for a number of revolutions (Say 10) That may give you a more accurate value for the pitch.

Les.

Edited By Les Jones 1 on 20/01/2023 14:21:44

The parts are from an old Webley air rifle. They are close to metric fine but are not metric fine. They are possibly a Webley thread. I'm getting the gun shop to try their contacts for further info.

Quick google of Webley thread sizes suggests it may be 11/64", certainly mention of 40tpi at that diameter and 48tpi taps and dies are also available

Jason,

Where did you the taps and dies are available ?

Came up on ebay after a search for 11/64 x 40 tap. It is US ebay that cam up so postage is high

post towards the bottom of this thread threaw up the 11/64 x 40

You might be able to advise, but I have never seen a screw thread (pipe threads specifically excluded here) where the actual measured major diameter is bigger than than the nominal diameter.

----

With respect to the tap mentioned later in the conversation, is it likely to be UN (60 degree) thread form?

Is there any standardisation of thread form among gunsmiths?

Oh oh, gunsmiths were notorious for non-standard threads!

I don't know why gunsmiths chose not to standardise: possibly it forced customers back to the maker for spares and repairs. Or maybe 'the old ways are the best' conservatism! Later the Royal Small Arms Factory stuck for years to the 'Enfield Inch' which is ironic because they were set up by government to overcome the extreme reluctance to modernise of the early Victorian British gun-trade, because they underperformed dismally before and during the Crimean War.

Dave

The thread is 0.180" x 50 TPI Whitworth, Finding a die to cut that should be interesting.

Parker-Hale in particular are notorious for this. Even two of the same part sometimes have different threads! 😬

I've successfully bodged a non-standard die by turning, threading and gouging a non-standard tap in silver steel, and then using it to thread a hole in a slice of silver steel, relieved by drilling two offset holes in it to create a die. (Might have plunge milled the holes as I vaguely remember the drill catching.)

Pretty crude but it worked well enough to make a few screws. I got the idea from the old guys who used a sort of plate:

I wonder if they chased the thread using some Whitworth Instrument thread chasers that they had to hand. That included 50tpi but on a smaller diameter (0.100" )

At least being an external thread that you need it will be easier to screwcut than an small internal one.

.

Useful snippet of information in post #10 here: **LINK**

https://www.airgunbbs.com/showthread.php?692569-Help-needed-with-Webley-Junior-Please

MichaelG.

.

Note: __ I was interested because I have a Junior pistol … early model 1929-1939

Edited By Michael Gilligan on 20/01/2023 19:55:03

Jason, The down side is at the other end of the screw there is an internal thread to accept a 0.106" x 50 tpi screw. Looks like time and history has beaten me. The blue printed diagram was drawn in 1938. Once the very limited supply of screws have gone that it.