triple-shouldered blind mortise and tenon joint

The triple-shouldered blind mortise and tenon joint is an L-joint that uses a tenon with three shoulders (setbacks) that engages into a correspondingly shaped mortise. The joint belongs to the tenon joint family and functions without additional wooden fasteners.
This joint belongs to the group of tenon joints and shows similarities with the simple through mortise and tenon and the Japanese Mechigai tenon. Comparable principles with multiple shoulders can be found in reinforced tenon connections and traditional frame joints.
The tenon is shouldered on three sides, creating three shoulders that enable precise positioning and increased contact area. The corresponding mortise is cut exactly to match the tenon dimensions. The connection typically occurs as a plug-in joint in L-form between two perpendicular timber pieces.
The triple shoulder formation significantly increases the contact area between connection partners and thereby improves load transmission. The precise fit prevents twisting and ensures high rigidity. The connection is self-locking and requires no additional fasteners such as wedges or dowels.
Traditionally, this joint is used in high-quality furniture connections, timber frame constructions, and structural carpentry work. Typical applications include purlins, sill plates, post-beam connections, and roof and wall structures.
Manufacturing involves precise marking and chiseling of the mortise as well as exact machining of the tenon with its three shoulders. The fitting work requires craftsmanship skills, as all surfaces must be plane and perpendicular to each other.