Koshikake kamatsugi

Known in English as bridle joints with wedge reinforcements, koshikake kamatsugi is an intricate traditional Japanese woodworking technique. It involves the use of thin wedges called "koshikake", which means cross-pieces, to strengthen the connection between horizontal floor beams and supporting vertical posts. These wedge-shaped reinforcements are cut so their grain runs perpendicular to both the beams and posts they are fitted between. When driven tightly in place, the opposing grain direction of the koshikake wedges interlocks with the beam and post fibers, locking the joint rigidly while allowing for wood movement. As a result, the bridle joints transfer weight stresses across the junction. With their grain running counter to the surrounding wood, the wedged reinforcements give the connections remarkable strength without bulk. This elegant joinery method endowed floors and frameworks within Japanese buildings like temples and homes with sturdiness to last for centuries under heavy loading.