New Gerber Stem / What do these rings do?

Hi. I received a new gerber stem kit. It came with 3 seats and these 3 plastic rings. 2 are black, 1 is white. Now, it feels like the white one goes on the diverter and the 2 black ones on the others, but the instructions don't seem to make mention of these rings. The stem that came out seemed to have the white one instead on the hot stem and almost like stretched slightly over the threading. Here are some pictures. The first is the stem with the 3 rings. The second is how it seems like it would go although I'm not sure what their purpose is. Can anyone clarify what do do with these rings? I'm only doing the hot stem by the way.

 

They are O-rings and they seal it from leaking between the stem and valve body. Water under pressure will work around the threads without the O-ring, If your kit is three stems, then the nylon O-ring would be used on the diverter valve. Do not over tighten the stems down or you can crush or tear the O-ring and you'll end up with a leak.

 

Thanks!