Bicycle Mechanics - Clipless Pedal thread size

I just bought the Speedplay Frogs for my mid-70's Bob Jackson road bike. Tried to install them yesterday but the pedal thread size on the Stronglight crank arms (made in France) is smaller than the Speedplays. Short of buying new crank arms, is there anything I can do? I knew I should've bought a new bike and not an older bike. But I just love hand-made frames made from Reynolds 531. Oh well.

arms are probably french threaded

May have to have the French crank arms re threaded to the other side of the channel fractional
9/16" rather than 14mm.. even the French finally adopted the English fractional standard
since the rest of the world , the market, has already gone over.

Thanks for the feedback. Where does one take crank arms to have them re-threaded?

Thanks for the feedback. Where does one take crank arms to have them re-threaded?
Any decent bike shop should have a tap to thread the crank to the 9/16" size. It's really close to the 14mm size thread you have now and the pitch is also very close so this is an easy procedure.

Kind of odd that while other industries were switching over to all-metric standards the bike industry standardized on English measurements for most of the key threads.

Pedal axles are 9/16X20TPI. A bike shop should be able to retap them for you.

Replacing the crank will have its own problems with the French sizing.

Replacing the crank will have its own problems with the French sizing.
Unlikely; Bob Jackson is an English builder and the bikes are English thread.

Bring it to Pinole and you can use my taps or I'll do it for you.

Thanks, all. Retapping sounds like the way to go.
Onward...