If a dimension between two components or subsystems inside precision machines or in complex test assemblies changes, readjustment may often be necessary. PIRest active shims, the piezo-based „washers“, offer a simple solution for it. Once they have been installed in the machine, the distance between two components or machine parts can be readjusted with their help and without any further assembly as often as required and with nanometer precision. These PIRest actuators have a high load capacity and they are long-term stable. This helps to reduce the installation time of high-precision machines and optical assemblies and it also reduces downtime, particularly in difficult to reach places (in vacuum chambers or inside machines). If active shims are already designed into the machine during initial construction, it already helps to save time and costs during the first adjustment.