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The term "bridle joint" is a woodworking term used to describe a joint in which a mortise is cut in one piece of wood and a tenon is cut in the other piece. The cut of both the mortise and tenon extends to the full width of the piece being used as a tenon. The mortise is a slot cut on one piece of lumber, and the tenon is a wooden tongue on the end of another piece of lumber. When cut correctly, the tenon will be received by the mortise and fit snugly without a lot of movement.
There are three variations on this joint: the basic bridle joint, the corner bridle joint and the T-bridle. All of the variations of this joint can be created with a hand saw and chisel using basic workbench construction skills. This has made the joint a popular choice among woodworking enthusiasts and carpenters. With the introduction of power tools — such as the circular saw, dado sets and electric routers — it has become much easier for woodworkers to create uniform joints, and this joint and its variations have seen even greater use.
The basic bridle joint is used to fit two boards together, one with a mortise cut and the other with a tenon cut. The corner bridle uses one tenon-cut board and two mortises that are half the depth of the tenon, joining the three pieces of wood together with a mortise on either side of the tenon to form a set of corners in the shape of the letter T. The T-bridle uses a mortise cut in the center area of the piece rather than the end.
The use of nails or other hardware that could rust and leave stains in the wood are not required in a bridle joint. Using friction alone, this type of joint is extremely durable when the component parts are cut correctly. For added durability, however, many woodworkers will also incorporate wood glue in the assembly process, gluing the three side of the tenon before inserting it into the mortise.
The bridle joint and its variations are used in many applications. The joint adds extra strength and durability to woodworking projects because it locks the lumber together, similar to the way that a jigsaw puzzle's pieces are connected. Some of the most common places where this type of woodworking joint can be found are hand railing uprights, picture frames, home construction and furniture.
Lap joints are similar in design to bridle joints, so the two types are sometimes confused. The major difference between them is easy to see upon closer visual inspection. The lap joint does not have a true mortise but is actually two tenons that are cut to half the thickness of the wood. Although this joint can be used effectively in many circumstances, the lap joint does not have the strength of the bridle joint. As a rule of thumb, the bridle joint can be used in place of a lap joint to provide additional strength to a project, but a lap joint should not be used in place of a bridle joint.