Locking rings, SGA, SGH, RS etc.

You can measure the size of locking rings or securing rings with the name SGA by measuring the outer diameter of the shaft. If it is 16 mm, you should have an SGA 16.
The same principle applies to internal circlips SGH, where you measure the inner diameter of the hole. If it is 16 mm, you should have SGH 16, you should not measure inside the groove.
When it comes to track riders "RS", you should instead measure inside the track, if the bottom of the track is 7 mm, you should have an RS7.