Shoes 2 and 2' turn about axis A and are connected by turning pairs C to rollers 4 and 4'. Lever 1 is connected by turning pair D to wedge 3. Shoes 2 and 2' are pulled toward each other by spring 6. Shoes 2 and 2' are forced against the drum of wheel 5 by wedge 3 which spreads rollers 4 and 4' when lever 1 is turned counterclockwise.
$2194$WL,Br$