Most bicycle pedals are interchangeable using 9/16″ x 24 TPI (Threads Per Inch) threading. So, you can screw pedals from a Raleigh onto a Fuji. Other threadings exist. The most common is American 1/2-inch x 24, used on one-piece steel cranks, also known as “Ashtabula” or “Wald” cranks. Another, formerly common threading, is French, which is 14 millimeters in major diameter by one thread per millimeter (known as “14 x 1”).
However, the left pedals are left-hand threaded. This means, they tighten in the opposite way. To install a left pedal, you’d turn it the way you’d loosen a jar lid. Countless cranks have been ruined by people who did not expect that there’d be a difference in left and right pedal threading and tried to jam the wrong pedal onto the wrong side of a bike.
The reason the left pedal is left-threaded is that in case anything goes wrong, if a pedal bearing freezes up, the pedals will unscrew, rather than risking injury of the rider. One could argue that a pedal totally unscrewing and falling off risks injury as well. But, if the rider has cleated shoes, or uses toe clips, the chance of hurting an ankle when a pedal fails is much greater.
Pedals come in many configurations, some requiring special shoes to match. Some pedals have rubber surfaces, allowing barefoot riding. Most are made from metal, generally lightweight aluminum alloy, with serrated surfaces, so the rider’s feet are not likely to slip. High-end bikes are often sold without pedals, since the rider will want to choose specific shoes and pedals.
when installing pedals, they should be tightened firmly. A light coating of grease on the threads is a very good idea. This insures that the pedals can be removed several years later. Pedals in aluminum cranks are particularly prone to stuck threads because the pedal spindles are made from steel. When dissimilar metals are in contact for long periods of time, they suffer galvanic action which leads to corrosion.