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The photo was from a site that no longer seems to be up. The pedal on the right, measuring at 15.7mm is the same size that the pedal on my indoor spin bike uses and I want to use standard 9/16 threaded pedals instead.
Has anyone come across this size??? Do adapters exist to step up standard 9/16 to 15.7mm?
Unfortunately, this might not be easy to find a solution for. The larger thread size doesn't seem to be a standard bike pedal thread, so finding a specific adapter is probably not possible.
Another solution might be to use some kind of threaded inserts in the cranks (this would probably require drilling the cranks out for a larger thread). But the standard pedal thread of 9/16-20 is not widely used anywhere else, so finding the inserts (let alone a left-handed ones is probably next to impossible.