I cannot get my head around this - as one of the previous posts says
Type - Inch - Metric
Italian - 1.378" x 24 tpi - 35 x 1.058 mm
ISO - 1.375" x 24 tpi - 34.92 x 1.058 mm
British - 1.370" x 24 tpi -34.80 x 1.058 mm
French - 1.366" x 25.4 tpi - 34.7 x 1 mm
Metric BMX - 1.181" x 25.4 tpi - 30 x 1 mm
why is it not British? and the F at the end also helped to confuse me too.
Sorry, the above list is correct, and I have corrected my previous post. British and ISO are essentially completely interchangeable and you could interchange ISO and Brit threaded freewheels on the same ISO or British hub. Italian will fit on to ISO and British threaded hubs, but if you screw an Italian freewheel on to a Brit threaded hub that hub will be forever only suitable for Italian freewheels. The initial action of screwing an Italian freewheel on to a Brit hub re-profiles the thread pitch and going back and forth will eventually weaken the threads to failure.