Why use shims?
There are three basic reasons for designing shims into assemblies and devices: Tolerance compensation. Shims eliminate the time and cost of putting precision tolerances on mating components. They also compensate for accumulated tolerances during assembly. It is better to design in a shim than to discover later you need one at the assembly stage. Precision alignment. Shims align parallel and angular surfaces when interfacing elements must be coupled. Wear compensation. Shims compensate for wear and are often designed to be the sacrificial component so the basic equipment retains its original accuracy.
