Hanna

almost all pedals for modern bikes are a standard size of 9/16 X 20. Unless you buy pedals for a child's bike, or some vintage French pedals (unlikely in clipless) you can be very confident that the clipless pedals you buy will fit.

I have ridden Shimano SPDs for years and really like them, in particular the "walkability" of the shoes and the "float" allowed by some of the cleats.

Be sure to grease the pedal threads when you install and remember - the left pedal is "Left hand threaded". "Righty loosey". Opposite of normal threads. Your shop will know this - but if you install yourself (it's easy if you have a pedal wrench) you'll want to know this.

good luck.

Mark Petry
Bainbridge Island, WA USA