Ostrolenk, Faber, Gerb & Soffen
Golf club head and a method for producing the same
 In production of a shell-type golf club head made up of several different pieces, an iron-type material of a specified chemical composition and carbon equivalent is subjected to a combination of annealing before shaping with quenching after shaping. Exclusion of the conventional casting process in production much improves mechanical characteristics of the product and increase mechanical strength enables formation of a large size golf club head with an enlarged sweet spot. Limited and locally specified disposition of weld lines assures highly accurate lie and loft angles with reduced welding strain. 
Yamaha Corporation
A C C A C A A A C
A63B C21D C21D A63B C21D A63B A63B A63B C21D
inventional additional additional additional inventional additional inventional inventional inventional
Kikuo Toshiharu Takashi Yuma Hiroyuki Kazuhiro
Nishida Hoshi Iijima Horio Yamashita Tsuchiya