If your portafilters are engaging too far to the right (and you don't want to buy new portafilters), you may want to consider purchasing the F_60, the 9mm gasket.

SEMI-COMMERCIAL MODEL USERS BEWARE!

Models such as the Expobar, ECM Giotto and Isomac claim to have an E-61 group head, and for the most part they are, but we have found that the inside diameter of these gaskets are too small, and recommend this other gasket instead: W_556