Wedge

A wedge is a simple tapered piece of wood or metal, doing one of two very different jobs in woodworking depending on context. Driven into a saw kerf cut into the end of a tenon protruding through its mortise, a wedge splays the tenon's end outward inside the mortise cavity, mechanically locking the joint permanently in place -- a wedged mortise-and-tenon, traditionally used on through-tenons meant never to be disassembled. Used instead for splitting green wood along the grain (riven, rather than sawn, stock), a series of wedges driven into a starting crack propagates the split cleanly along the wood's natural grain line, a technique that predates the saw by a considerable margin and is still used in green woodworking and chair-making today.