Re: Freewheel Query
take it away Sheldon:
Freewheel Threading
The standard ISO threading for freewheels is 1.375 x 24 TPI, the same as for standard ISO bottom brackets.
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
All recent freewheels and threaded hubs, regardless of where made, use ISO threading. The older British and Italian standards use the same thread pitch but a very slightly different thread diameter, and are generally interchangeable. However, for strong riders and on tandems, it is best not to mix and match -- freewheels sometimes do strip the threads of aluminium hubs. A French freewheel may start to thread onto an ISO/British/Italian hub but will soon bind. An ISO/British/Italian freewheel will skim the top of the threads of a French hub and will slip forward if an attempt is made to use it. Do not force a freewheel -- you will ruin the hub.
A bottom-bracket cup can serve as a thread gauge for a freewheel: Dimensions are usually marked on cups. Hold the threads of the bottom-bracket cup against those of the hub, and look in between, against the light. If the threads engage tightly all the way across, the thread pitch is the same. If they rock across each other, it is different. You may check the thread pitch of a freewheel by threading an ISO left bottom-bracket cup into it (not a right cup, which is left-threaded). The cup will go in easily if the thread pitch is the same -- but do have a freewheel extractor tool handy so you can unscrew the cup.