One more, what;s the difference between KV3GR E1 and KV3GR E2 heads?

Also my ring gap is 0.50mm and there is "NO DATA AVAILABLE" for MC18 model, I assume since service limit on all others is 0.5 it it should be same/similar on MC18 so these need to be replaced?

EDIT, one ring is .50, others are 0.45-0.47 mm