Bicycle Mechanics - English thread freewheel to fit Italian thread hub?

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robertmccormack
11-10-07, 07:10 AM
I just purchased a NOS freewheel style Mavic 550RD rear hub sight unseen which the seller claimed had English threads. It turns out that they are actually Italian thread 35mmX24 tpi. Will I be able to fit a normal English thread Shimano freewheel onto the hub? I haven't tried because I want to be able to give it back without scratches for a refund if it doesn't fit.

nowheels
11-10-07, 07:14 AM
No....
well biked
11-10-07, 07:21 AM
Sheldon says the only difference is the thread pitch, and it will work. But once you do that, it seems you shouldn't go back and forth between English and Italian threaded freewheels. Look in Sheldon's glossary under "Italian," he discusses it there.

HillRider
11-10-07, 07:38 AM
Sheldon says the only difference is the thread pitch, and it will work. But once you do that, it seems you shouldn't go back and forth between English and Italian threaded freewheels. Look in Sheldon's glossary under "Italian," he discusses it there.

The difference isn't exactly the thread pitch (i.e. the number of threads per inch) which is the same, but the thread form. English threads have a 60° included angle while the Italian threads are 55°. As noted they will work with each other but once you make the change, stick with the new thread form.
well biked
11-10-07, 07:42 AM
The difference isn't exactly the thread pitch (i.e. the number of threads per inch) which is the same, but the thread form. English threads have a 60° included angle while the Italian threads are 55°. As noted they will work with each other but once you make the change, stick with the new thread form.


Ah, I was confusing pitch with angle, thanks. For the record, Sheldon didn't say pitch, he said angle.
robertmccormack
11-10-07, 08:09 AM
Thanks for the advice. I checked out Sheldon Brown's glossary, and he adds that since Italian freewheels are basically extinct, the issue is moot there. After hearing from you, I greased the threads and slipped on the freewheel-- it fits no problem. You're the best!
robertmccormack
11-10-07, 08:18 AM
Right, thanks. Btw, for anyone else interested in this issue, I found the following on CampyOldy.com:
Will a freewheel fit English/BSC and Italian thread hubs?

It is my personal opinion that if any freewheel will screw on the intended hub using only your fingers then it is satisfactory. There are 25.4mm = 1”. Italian hub thread is 35mm diameter. English is 1.370; multiply that by 25.4 = 34.798mm. Both are 24 teeth per inch.