Pair of rear suspension thick spacer shims. These shims have several uses. Some modern, rear suspension units, such as BGM and Mupo, have thinner-than-standard silentblock 'knuckle' bushes, and these spacers take up any excess play. 

Some rear suspension units can also touch the rear mudguard on the inside, and a pair of these spacers is enough to distance the shocker away.

Most 80s and 90s Serveta models use longer-than-usual pins, on both the frame and motor, for the rear suspension unit. If the suspension unit is replaced with one that has normal width knuckle bushes, you'll need at least 3 of these spacers at both the top and bottom to eliminate the excess of the protruding pins, as can be seen in the pics. Hence the reason why we sell these in sets of 6 pieces.