How do you tell what size bmx pedals you need?

Answer 1

1 piece cranks need the 1/2 inch pedals while 2-3 piece cranks use 9/16th.

Just to help the newbies out there. OPC or one piece cranks mean the arm that holds the pedal is just one piece of steel that goes from pedal to pedal through the bottom bracket (where the bearings ride). Those only use ½" size threads on the pedals.

3 piece cranks are identifiable as each arm is separate and bolted onto the spindle which is part of the bottom bracket. 3 piece refers to 2 arms + the bottom bracket. Only 9/16" (which are bigger than the ½") threads fit those arms.

Don't forget the left arm is backwards thread, so to loosen you turn it righty tighty. The right arm is normal so lefty loosy to remove.