Leybold WA/WAU 151 & 251 Booster Vacuum Gauge Disc (0.20),50x62x0.20mm, PN ES22105161
These stainless steel gauge discs are stacked in various combinations, and resultant thicknesses, to shim and adjust motor rotor spacing on the bearing plate end of Leybold WA/WAU 501 vacuum pumps.

Note that this particular gauge disc, PN ES22105161, is 0.20mm thick, and may need to be used in combination with any of the appropriate gauge discs listed below. Please refer to manufacturer documents and the table, below, for details.