According to Sutherland's your old Schwinn cranks probably are probably tapped old USA standard 1/2"x20 TPI. The current standard is 9/16"x20 TPI. You can probably double check this by heading over to Home Depot and try threading a 9/16x20 nut on the pedal threads. Sutherlands offers this tip: When retapping pedal threads, start from the back of the crank arm. Hope this helps.
Regards,
Raymond
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