Quote Originally Posted by Catrin View Post
I have decided to purchase the M540 pedals, they are just a little more expensive than the M520, and they are lighter - though seem the same size so it must be the materials.
The M520 uses a plastic sleeve between the bearings and the pedal body. There are some web pages claiming that the plastic sleeve breaks after not all that many miles of riding.

The M540 uses a metal sleeve instead of the plastic.

Shimano has a number of pedals built with each technology. The plastic sleeve has 10 ridges and needs a special tool to grip it. The metal version is hex sided and a standard wrench is all that's needed.