Correct orientation of metal disc in front brake master cylinder?

[2BRacing]

I am getting a GS650G baby Katana ready for the road again after standing for a long time, and replacing all the rubber parts in the front and rear brakes.

When I took the front master cylinder apart, I did not take proper note of the orientation of the shiny metal disc that is located between the piston and primary cup/spring.

That shiny copper-coloured metal disc (not sure of proper name?) is not flat, but has a "hollow" side and a "rounded" side.

What is the correct orientation of this disc: with the "hollow" side against the piston, or with the "hollow" side against the rubber primary cup on the spring? Not sure if it will make a difference, but I would like to get the orientation correct. Thanks!


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[chuck hahn]

usually there will be some light witness marks on the piston side of the disc if you really want to know what side was what.

[2BRacing]

usually there will be some light witness marks on the piston side of the disc if you really want to know what side was what.

After inspecting the disc with a magnifying glass, I did find some marks indicating that the hollow side was against the rubber primary cup. The disc in the new OEM piston kit also had a "hollow" side (looking like a half moon), so I installed it like that again.

Thanks guys!