Screwfix ball valve

[bmetcalf]

From http://mdmetric.com/tech/tic1e.htm

4. MOST METRIC COUNTRIES IN EUROPE AND ASIA USE THE BRITISH BASED INCH SYSTEM (ISO) FOR MEASURING NON-HYDRAULIC/PNEUMATIC PIPE AND TUBING THREADS. SOME EXAMPLES OF THESE THREAD DESIGNATIONS FOLLOW:
THREADS EQUIVALENT TO BSPP/BSPF (BRITISH STANDARD PIPE - PARALLEL) ARE DESIGNATED IN GERMANY AS: G 1/4; IN FRANCE: G 1/4 cyl; IN JAPAN: PF 1/4; IN BRITAIN: R 1/4 Tr.
THREADS EQUIVALENT TO BSPT (BRITISH STANDARD PIPE - TAPERED) ARE DESIGNATED IN GERMANY AS: R 1/4 keg; IN FRANCE: G 1/4 co; IN JAPAN: PT 1/4; IN BRITAIN: R 1/4.
THE REFERENCE STANDARDS FOR ISO R228 PARALLEL PIPE THREAD ARE DESIGNATED AS: GERMANY - DIN 259; BRITAIN - BS 2779; JAPAN - JIS B 0202
THE REFERENCE STANDARDS FOR ISO R7 TAPERED PIPE THREAD ARE DESIGNATED AS: GERMANY - DIN 2999; BRITAIN - BS 21; JAPAN - JIS B 0203

 

[Tom Gaynor]

Thanks, Bruce, that's seriously useful, because I spent ages trying to identify the threads on taps shown on websites, and all they said was stuff like "1/4". Ah!!! 1/4" as in "1/4" BSP (aka "gas"), a thread suited to a nominal 1/4" bore pipe...

 

[bmetcalf]

Not exactly (at least for US sizes), see http://www.usaindustries.com/pipe_schedule_chart.htm