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

SEMI-COMMERCIAL MODEL USERS BEWARE!

Models such as the Expobar, ECM Giotto, Isomac and Quickmill claim to have an E-61 group head, and for the most part they are, but we have found that these gaskets are a bit too tight on the inside diameter. We recommend you contact your dealer (or someone who sells the units new) for the specific gasket for that particular unit.