938275598 approx 31.4mm OD x 3.7mm thick oring
If your 750F1 has a smooth piston that sits in a 31mm bore, and in that bore is an o-ring... This is that oring. We finally found 1 that fits, it works, and it lasts.
750 Paso, 750 Sport etc also take this same o-ring assuming you have a 31mm bore in yoru clutch cover that the clutch piston slips down into.
I suppose this is the same as The Mille piston
Reviewed by Hedton on 10/28/2023
i've written about this here.
https://forum.bevelheaven.com/viewtopic.php?f=10&t=5178
The Mille has two grooves.
I use these orings
31.34mm X 3.53mm for the lower one.
31.42mm X 2.62mm for the upper one.