Mortise and tenon

A mortise and tenon is a woodworking joint that connects two pieces of material — typically wood — at right angles or in-line. One piece has a rectangular hole (the mortise) and the other has a corresponding projection (the tenon) that fits snugly into it. The joint is one of the oldest and strongest in woodworking, used for thousands of years in furniture, timber framing, and door construction.

The two parts

• Mortise (sometimes spelled mortice): a cavity cut into one workpiece, usually rectangular in cross-section. It may be through (going all the way through the board) or blind (stopping partway).
• Tenon: a tongue-shaped projection on the end of the mating workpiece, sized to fit the mortise precisely. Its shoulders — the flat surfaces where the tenon meets the rest of the board — register against the mortise face and absorb racking forces.

Why it is strong

The joint’s strength comes from its large glue surface and mechanical interlock. The tenon is trapped on four sides inside the mortise, resisting forces from multiple directions. Unlike a butt joint or a dowel joint, the mortise and tenon does not rely on fasteners alone — the geometry itself holds the pieces together. For additional security, a drawbore pin (an offset dowel driven through both pieces) can pull the joint tight without clamps.

Common variations

• Through tenon: the tenon passes completely through the mortise piece and is often wedged or pinned on the exit side.
• Haunched tenon: a small shoulder is left on one edge to fill a groove, common in frame-and-panel doors.
• Bridle joint: an open mortise-and-tenon where the mortise is cut as a slot across the end of the board.
• Loose (floating) tenon: a separate tenon piece inserted into mortises cut in both workpieces — easier to execute with modern jigs.

In Chinese woodworking

The mortise-and-tenon tradition is called 榫卯 (sǔnmǎo). Chinese carpentry developed dozens of variations — some purely interlocking without glue or nails — used in architecture, furniture, and boat-building for millennia.