Quote Originally Posted by laura* View Post
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.
Hm, good to know! I'm bouncing between SPDs and Speedplays, at the moment, so if I go the SPD route, I think I'm going with the M540...