bsa 310 Cadet QUestion please

Hope this is not too off the wall but-- what is the screw size and thread for the barrel sight on an Australian Cadet, please?

I think you will find they were .096 x 56 TPI a 3-56 TPI should fit being .090 x 56

Just love "Industry Standards";

There are so many to choose from!

Good point about the 3-56; the only catch will / may be that "Enfield" /"gunmaker specials" are probably more like 49(ish) degree form as opposed to the 60deg of the 3-56.

Yes very true Bruce.
One wonders why they weren't a bog standard (as Peter L would say) BA thread.

Dick

Because RSAF Enfield, and the "Trade" wanted a Monopoly on both screw manufacture and repair of their Firearms...a form of "Gun Control ante-diem" in Colonial Empire.

Hence the "Enfield Inch" and the Un-standard TPIs and diameters...but the Brits are not alone, S&W (USA) screws are also "Strange".

But by 1926, the Brits saw the Light, and the Mark VI/Rifle No.4, was made with standard BSF and BA screws (Brit.Standard Fine (1/4 inch up) and British Association ( less than 1/4 inch)...Instrument and clockmakers threads.
Webley is also another with "strange" diameters and Tpi. and items such as Tripods etc, used "British Cycle Threads"....

But the Germans were not immune...Mauser used a 1/4inch x22 Tpi Receiver screw for every Rifle from the M67/69 Norris Mauser through to the Kar98k ( Not a British "standard", but widely in Use in Liege, where Mauser did some work in the late 1860s...also Mauser Barrel Threads were "Withworth Form" (55 degrees) and 12 tpi.)

And of course, the Berdan II and the Mosin Nagant, were all "Withworth" form and tpi...from 1891 to the Chinese Mosins of the 1960s....Despite "metrication."

Doc AV

Type 38 Arisakas are full of Imperial threads, Type 99s are thoroughly Metric.

I think it was the case that Enfield had their own screw system before Whitworth got around to standardising, and never saw a reason to change. One of the few Enfield threads that is still around is the one used on Parker Hale cleaning rods and brushes. It is the same thread that is on the P53 Enfield ram rod and the Martini Henry clearing rod..

I understand that the Singer Sewing Machine company was the same in using their own thread system... at least while their cast iron machines were still being made.
I understand the reason for Mosin Nagant and Arisaka rifles using Whitworth threads is that many were originally made on contract in Birmingham (UK) and that most of the machine tools used in the Tula arsenal were made by Greenwood and Batley in Leeds. The 7.62 barrel used in the Mosin is to all intents and purposes, a .303 barrel!