These hammers are known as Genno in Japan. The Maru Gennou hammer is an excellent carpenter's hammer for general use.
 
The faces of the heads are slightly convex on both sides. The head's hardness is HRC55-60. It has a Tsuchime finish. Tsuchime (hammered) finish, or Tsuchime pattern, is a traditional Japanese artisanal finish, made by hammering the metal sheet one pattern at a time.
 
*Because the handle is made of natural wood, the colors and patterns vary.