bridle joint

The bridle joint is an L-joint where one member is provided with a fork-shaped slot into which a tenon-shaped end of the second member engages. The connection creates a form-fitting corner joint without additional wooden fasteners such as wedges or pegs. Both members are weakened in such a way that symmetrical force distribution occurs, with the tenon inserted into the open fork.
This joint belongs to the tenon joint family and is also referred to as an open mortise and tenon. It shows similarities to the open slot mortise joint and the Japanese sammai-gumi. Unlike the enclosed mortise, the slot here is open, allowing the joint to be assembled from the side. This characteristic feature enables simpler assembly while maintaining good force transmission.
The geometry consists of a fork-shaped slot that divides approximately one-third of the member width into two parallel cheeks. The opposing tenon is cut to the corresponding width and thickness so that it fits exactly between the two cheeks. The tenon can be flush with the outer surface or pass through. The shoulders of the tenon rest against the end faces of the cheeks and transmit compressive forces, while the tenon itself absorbs shear forces.
The bridle joint offers a robust and easily manufactured corner connection with good force transmission. The open construction allows simple assembly without complex mounting techniques. The connection can be executed without metallic fasteners and is suitable for right-angle connections at various angles. However, the notching significantly reduces the load-bearing capacity of both members. The open fork is susceptible to lateral forces and torsion. With improper fabrication, the joint can develop play and lose strength.
Traditionally, the bridle joint is used in roof construction for rafter connections to sills and plates. In furniture making it is used for frame constructions in tables, chairs, and doors. In timber-frame walls it is employed for rail connections. In interior construction it is used for door and window frames as well as load-bearing frame constructions. The joint is particularly suitable for constructions where members meet at right angles and moderate loads must be transferred.
Fabrication is carried out by precisely marking the fork and tenon, accurately sawing the parallel slots for the fork, and cleanly chiseling out the intermediate space. On the tenon member, the shoulders are marked and the protruding material is sawed off. Fitting accuracy is crucial for the strength of the connection. For visible applications, careful surface finishing is required. The joint can be subsequently secured with wooden pegs or screws, though traditionally it is executed without additional fasteners.