Bought this superfine 12ga chamber brush on Amazon. $20 (delivered from England, I think.)
The fool thing has no known threadpitch on earth. (That assumes the UK is not part of earth.)
I believe the Bisley/Parker-Hale shotgun cleaning rod thread specs are closely guarded national secrets, kept in James Bond's sock drawer, as I have searched an inordinate amount of time to find the actual thread size, to no avail.
It appeared to have 24 tpi and a 7mm diameter. Try finding a 1/4-24 tap. Hah.
Tried an m8x1.25, which I had in stock. Too loose and will not thread on fully.
So I bought an m7x1.0 tap and 6mm tap drill. No dice. Threads on partially, but then locks up.
I just ordered a
1/4-26 British Standard Fine (BSF) taper tap from Amazon. Here 1/11/23.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
The BSF standard at
https://britishfasteners.com/threads-bsf says to drill a No 6 hole.
There is a BSC (British Standard Cycle) thread spec, too, just to add to the crazy.
https://britishfasteners.com/threads-bsc. The link says to drill a No. 3 hole before tapping for the 1/4-26 BSC thread.
And just for fun, there is also a British Standard Brass spec.
BSF, BSC, BSB (fine) and BSW (coarse) all have a 55-degree angle.
Oh, and a BA (British Association) spec, with a 47.5-degree angle.
https://newmantools.com/taps/tapsbritish.htm
All four British specs are different.
"Commonly knows [sic] as British Size or Whitworth Thread this was the thread system used by Great Britain and the British Colonies before 1970.
The United Kingdom adopted the Metric system in the 1970's."
Except for shotgun cleaning rods. They kept to the Old Ways, I guess.
I'll keep you posted.