Waters Autospec Premier Operator's Manual page 186

This spacer is shaped, and will fit only one way round.
Tip:
Repeller contact ceramic spacer
6. Fit the repeller contact over the repeller shaft.
Repeller shaft
Repeller contact
7. Fit the nut and washer securing the repeller contact to the repeller. Do
not tighten the nut fully at this stage.
Use the "clutch pencil" tool to place the nut on the repeller's thread.
Tip:
Caution:
otherwise the instrument will not function.
7-28 Routine maintenance
The repeller plate must not touch any part of the ion block,