A shower screen (dispersion screen) mounts in the grouphead itself and spreads incoming water across the puck. Unlike baskets and tampers it is keyed to the grouphead, not the portafilter diameter, so fitment is machine- or group-specific (e.g. E61) rather than by portafilter size.
These fit by grouphead rather than portafilter size.
New to sizing? See espresso portafilter sizes explained, or browse all part types.