Until now, i found out there are many airsoft gun made by KSC/KWA use same piston head.
From picture above, from left to right
First is piston head/ring for KSC glock series, only Glock model use this piston.
Now the second one, is for KWA Mp7, KSC M9 also using this piston head. I think KSC M93r also use same piston head. But haven’t confirm it personally.
The third one, color in yellow. This piston head use in USP series, M1911, and in P226.
The last one, the biggest piston head is for KWA Kriss Vector.
I hope this information is usefull.