Canvas Keys or Wedges! What are they and how to use them?

Keys/Wedges are those little pieces of wood that you generally find in a little plastic bag attached to your box canvas.

These bits of wood are canvas tightening keys or wedges, used if the canvas begins to sag a little on the stretcher. This can happen over time due to temperature changes, humidity, and aging. You place them into the slots made for them in the corners of the stretcher bars and tap them in further to tighten or square up the canvas. Most canvases that come with canvas keys come with eight of them, two for each corner.

How to Use Canvas Keys

If you find that your canvas has become loose or sagging, slide the canvas keys by hand into the slots in the stretchers in the corners.



  • The wedges are shaped, pointed on the end, and longer on one side. The pointed end goes into the slot, some people put them in with the long side flush against the side of the stretcher bar, while others prefer to place them with the short side against the side of the stretcher bar so that the wedges are angled out toward the center of the canvas. Try both ways and decide which works best for you.
  • Place a small piece of cardboard between the canvas keys and the canvas to protect the canvas when you tap the wedges into place with a hammer.
  • For a smaller canvas, you can gently tap the end of both wedges or keys, into the corner with the hammer, working your way around to each corner. You may see the mitered space at the corner of the stretcher increase as you tap the wedge.
  • For a larger canvas, in order to keep the tension on the canvas even,  you will want to push out the opposing stretcher bars first. In order to do that you will tap the wedges that push a stretcher bar in one direction, then rotate your canvas so that you can tap the wedges that push the opposite stretcher bar in the opposite direction. Then do the same for the remaining sides.
  • You may need to go around again, but you don’t want to knock them too hard at first. You run the risk of splitting the wood of the stretcher or over-correcting. By gently tapping the wedges you will eventually achieve the desired tautness of canvas.

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