Originally Posted by
freeranger
Buy the wrench according to the size of the FLATS on the pedal spindle, not the thread size. I use a 15mm which is the size of the FLATS on the pedal spindle, all of my bikes are this size. Do you have pedals with different size flats, which is the way I read the original post? If you have a pedal which has 1/2" FLATS, you'll need 13mm.
1/2" refers to the thread diameter (1/2" x 20tpi), not the distance across the flats, just as 9/16" (14.2875mm) refers to the thread diameter (9/16" x 20tpi), not the 15mm distance across the flats. Most modern pedals are 9/16" x 20tpi and use a 15mm wrench (or 6mm Allen key). 1/2" pedals, still used on many stationary exercise bikes, children's bikes, and some department store bikes will likely use a 9/16" wrench.
Curiously, my Zeus pedal wrench is marked 15mm on one end and 14mm on the other.