hidden mortise and tenon with beveled shoulders

The hidden mortise and tenon with beveled shoulders (Fensterriegelzapfen) is a T-joint that uses a hidden tenon with beveled shoulders. The connection remains invisible from the outside and transfers loads through both the tenon and the shoulder surfaces. It functions without additional wooden fasteners.
This joint belongs to the group of tenon joints and shows similarities with the Japanese Oire (beveled shoulder mortise and tenon) and other concealed tenon connections. Comparable principles with beveled bearing surfaces can be found in stepped tenons and reinforced structural connections.
The tenon is inserted into a corresponding mortise, while the beveled shoulders meet specially machined bearing surfaces. The beveling of the shoulders enables better load distribution and prevents slipping under load. The concealed execution ensures a clean external appearance without visible connection elements.
The beveled shoulders distribute loads over a larger area and relieve the tenon, achieving higher load capacities. The concealed construction offers aesthetic advantages for visible components. The precise fit of all surfaces ensures high rigidity and dimensional stability.
Traditionally, this joint is used in window and door construction, high-quality furniture, and traditional architecture. Typical applications are rail connections, door frames, window frames, as well as interior construction and wall structures where both structural and aesthetic requirements must be met.
Manufacturing requires precise craftsmanship. Both the mortise and the beveled bearing surfaces must be worked exactly. Tolerances between tenon and mortise as well as between shoulder surfaces must be kept minimal to ensure optimal load transfer.