Kabuto arikake

Kabuto arikake is a unique Japanese woodworking joint known in English as "helmet overlay". It features a thin "helmet" piece of wood shaped to fit over the ridge of a roof beam where it meets a horizontal purlin or rafter.

Most commonly used in traditional Japanese roof framing systems, the helmet wood is cut with its grain running perpendicular to the beam it caps. Through precise fitting, the end grain of the helmet piece is tightly fit over the top grain of the angled beam below it. This creates an extremely strong junction that helps distribute forces across the overlapping grain. 

By reinforcing the critical ridge joints of roofs with kabuto arikake's interlocking wood-on-wood connection, master carpenters were able to construct durable roof structures able withstand harsh weather for centuries. Even today, its distinctive counter-grain overlay remains an elegant solution for joining roof members through natural stiffness rather than mechanical fasteners.