Brake piston ring? ('76 Z750B1)

Hi guys. Just got some new brake pistons since the old ones are pretty worn.. When I took them apart there were two metal plates insterted in the piston and secured with a ring (first piece from the left). But when I put this ring on the new piston, it goes on too easy...I'm not happy with it..I'm scared of this ring coming off while riding and jamming the brake somehow..what is the purpose of these circular plates? Can I assemble the brake without them (I don't have them on my 2004 Yamaha)?

Here are the parts...assembled piston on the right and exploded view on the left.

Anyone? :dry:

You don't need those plates. Very few pistons use them.

How where they worn...pitted, scored etc? never heard of em worn. usually the seal goes long before any metal wear. R

I looks that I deformed them a bit when taking them off the old pistons :S ... I will try without the ring and plates first. I think that it sould work, otherwise I will have to come up with something.