Originally Posted by stronglight

Some PX-10s which were imported to the US in the 1970s were specified for standard 9/16" pedal threads. They were often (but not always) marked on the back of the crank arm "9/16 - 20" along with the length of the arm in millimeters, such as "170". Even when un-marked, or even stamped "14x125" (indicating French threads), they were often modified after purchase by local bike shops. You can test a standard pedal on the crank. If it is threaded for standard pedals it may actually fit, although perhaps tightly after all these years, so be sure to use a bit of grease on the threads.