saoshachitsugi 竿車知継

Also saotsugi 竿継. Joint with long, rather slender tenons called saohozo 竿ほぞ (rod or pole tenons) and mortises called saomichi 竿道.
A straight drop-rod joint with keys *shachi 車知 used to join two timbers. Blind or stub tenons mechigaihozo 目違ほぞ and regular tenons cut into either side of the joint add extra strength. Haunched mortises are cut in both male and female sections to form slots into which the keys shachi can be driven. Sanbōhako mechigai saoshachitsugi 三方箱目違竿車知継 refers to a 3-faced boxed blind rod timber with keys. The mortise has a square blind U-shaped tenon cut on the face. A haunched rod tenon and the U-shaped cavities fit into the mortised part and keys are inserted.