What is a Mortice and Tenon joint?

Mortise and tenon A square hole with a square peg. If you look at a wooden table or chair. The leg has the mortise and the side rails have the tenon. The mortise is a rectangular hole slightly smaller than the width and thickness of the rail. On the rail, it extends past the visible length probably about 1 inch. This varies depending on the construction. This extension is between 1/8 to 1/4 of an inch smaller on each side than the rail. It fits into the mortise. Makes for a very strong joint.

Mortise and tenon joints are also used in post and beam homes and timber frame homes. As the most common timber framing joint, the mortise & tenon is versatile and functional. It is used to fasten connectors, posts, collar ties, struts, etc. The tenon can vary in size from 1-1/2" thick by 4" long to 3" thick by 10" long, depending on the load requirements of a particular joint. It is held tight by hardwood pegs.