Genno - that's what the Japanese call these hammers. The selective hardening of the actual hammering surfaces means that part of the recoil energy is absorbed by the slightly softer core. While one is hitting the work with the hammer one has the feeling that the stroke is more effective, and the reason is that less recoil affects the wrist. There are several essential differences between a Japanese and a Western hammer. Generally, although various cross section shapes are available, it remains just the one basic design. The Japanese hammer is very much a do-it-all tool; from driving nails to striking chisels (hence the iron hoop on the top of Japanese chisels). One face is flat, this is for driving nails and striking chisels, the other face is slightly crowned, used mainly for the final blow to the nail head thus driving it flush without damaging the surrounding surface. In Japan, metal hammers are traditionally used even to hammer chisels 7 Weights to choose from including: 4oz, 6.5oz, 12oz, 13oz, 16oz, 20oz,