US Patent 7198575 Golf club head

A golf club head comprising an outer shell and a strike plate having a strike face. The outer shell and the strike face define a club head volume. A heel/toe axis extends through the center of gravity of the club head. The heel/toe axis is generally parallel to the strike face and generally horizontal relative to a ground plane when the club head is at an address position. The rotational moment of inertia about the heel/toe axis is related to the club head volume by the equation Ixx ≧,46*HV+77, where Ixx is the rotational moment of inertia about the heel/toe axis in units of kg-mm2 and HV is the club head volume in units of cm3.