Originally Posted by
Leisesturm
Unlike a lot of things that screw into a bicycle, pedals are not something you have to worry about. All pedals have the same threading. All. I forget the thread pitch but you use a 15mm open ended wrench to install them. And the pedals on the left side of the bicycle ... you spin the wrench clockwise to remove (loosen)! And counterclockwise to tighten! This is vitally important to remember.
Not wholly correct as far as all pedals having the same threading but typically these days most adult bikes are 9/16" and many kids bikes are 1/2" but there were other standards and back in the day probably most of which have since bitten the dust. Some pedals also use a 6 or 8 allen key in the back to tighten rather than a flat that would use a 15mm pedal wrench.
Also anything with metal on metal contact use grease!!!!!!! If it is titanium use anti-seize/copper paste. Seized pedals (as well as seatposts) are no fun for anyone to deal with.