BEST Fittings Fully Rebuildable Buddy Bottle Valves designed and configured to fit Theoben Rapid, NOT suitable for Theoben MFR.
Stainless Steel, fully rebuildable.
M14 x 1.5 Valve suits the Luxfer 200/280cc Aluminium flat bottomed Buddy Bottles.
M18 x 1.5 Valve suits the Luxfer 400/500cc Aluminium flat bottomed Buddy Bottles.
If you have a steel Buddy Bottle with a rounded bottom it will be more than 10 years old and it will have a non standard BSP thread. We would advise renewing the bottle as a complete unit rather than attempting a valve repair.