US Patent 8727908 Golf club head

A golf club head with a hollow comprises a face portion whose front face defines a clubface for hitting a ball, the face portion comprising a central thicker portion provided in a center region thereof and a peripheral thinner portion provided around the central thicker portion and with a thickness smaller than that of the central thicker portion, the inner surface of the peripheral thinner portion comprising a first region and a second region, the first region being provided with a plurality of first grooves which extend straightly in a certain direction, and the second region being provided with a plurality of second grooves which extend straightly in the different direction of first grooves.