Term: Wedge

A thin piece of wood with a triangular end that is pressed into the corner slots of a wooden stretcher to tighten the canvas support. In order to expand the stretcher (referred to as keying-out), the wedge is gently driven into the joint with a hammer, pushing the stretcher bars further apart thus increasing the tension on the fabric.

Wedges are not normally added to a stretcher until the canvas has aged and begins to sag due to seasonal expansion and contraction. Purchased canvasses almost always come with a few wedges but they can also be purchased separately if needed.