sliding clutches

 

These generally have two shoes retained by circular springs on the flywheel. The shoes and the flywheel have interlocking grooves or guides. These grooves/guides then force the shoe to slide outward when subjected to the centrifugal forces of the rotating masses.

The flywheel of a Fioroni Sliding Clutch for an Kyosho MP 7.5
Note the 2 ridges which guide the shoes.
A four point clutch shoe for the Fioroni sliding clutch.
Note the grooves which fit on the ridges of  the matching flywheel.