Patent ID: 7018303

Claim:
A golf clubhead comprising a face portion having a back surface, said back surface provided around a center region thereof with at least two annular grooves so that said face portion is provided with at least two annular thin parts each being thinner than the center region and at least one rib part between the thin parts, wherein between said at least two annular thin parts and said at least one rib part, corners are rounded by an arc having a radius (r) in a range of 2.0 to 4.0 mm so that the thickness of the face portion changes smoothly, and also, in the annular thin parts, corners are rounded by an arc having a radius (r) in a range of 2.0 to 4.0 mm said center region has an oval shape having a minor axis of at least 10 mm extending in a crown-sole direction, and a major axis of at least 20 mm extending in a toe-heel direction, in a cross section of the face portion, said at least two annular thin parts and said at least one rib part are formed by a sine-like curved line in a vertical direction, and in a horizontal direction by a curved line that is a hybrid of a sine wave defined by said at least two annular thin parts and a trapezoidal wave defined by said at least one rib part.