Hi Graeme,
Most of the cycle threads (called, by the way, BSC, BSCy, or occasionally CEI) will be 26 tpi from 1/4 to 1/2". However watch out for the occasional 20 tpi thread in sizes like 7/16 or 1/2" - these are also cycle thread even though you will be told they are American UNF). As Rex suggests you might also find some BSF. BSW will only appear where threads are tapped into aluminium alloys (crank case end of barrel studs, base of magneto) and maybe a few 1/4 odd bods here and there.
The hexagon sizes are likely imperial (BSW/BSF).
Leon