Also called iriwa 入輪. Lit. a collar ring. A collar tenon. It has a step-like piece called a collar, cut on each side about two-thirds of the distance from the tenon to the edge of the beam. The mortise into which the collar tenon will be attached at right angles is cut from the inner side of a beam. The matching mortise is called eriwa-ana 襟輪穴 (also iriwa-ana 入輪穴). Since the two parts are joined together at right angles, this belongs to the broad category of joinery called *shiguchi 仕口. This type of tenon is sometimes combined with haunched tenon *konehozo 小根ほぞ, which has a smaller tenon on the tip of a larger one, used especially when joining wooden parts of mud sills *dodai 土台 in a grid pattern. There are many types of collar joints. One further example is the eriwa konehozosashi 襟輪小根ほぞ差, or collared haunch mortise.
