A Japanese chisel, or nomi in Japanese, consists of a hard blade, called hagane attached to a softer piece of metal called the jigane. Here’s a collection of Satoshi’s chisels.
All of Satoshi’s chisels are “set up” by himself. This process is called shikomi. The metal ring attached to the handle is removed and then the wood handle is filed to loosen the handle so the ring slides further down towards the blade. And finally, the wood is beaten down around the metal ring.
The metal ring ensures the wooden handle does not split and this way the ring never falls off the wood handle either.
The center chisel in the photo is before the shikomi and the chisel on the right is after shikomi (in fact after many years of use).