10 mm diameter, 26 threads per inch 141 mm length.
This size fits older Campagnolo and many other Italian rear hubs made for threaded freewheels or track sprockets. (Avocet, Ofmega, Miche, Zeus, etc.) and is the correct length for frames with 130 mm spacing
We stock Wheels, Inc. axles in this threading. These are very high quality U.S.-made