What are canvas keys?

My canvases arrived today, and stapled to each one was a familiar little plastic bag containing 8 little pieces of wood. Every time I've bought ready-stretched canvas, I've always wondered what these things are, and how to use them. So I thought I'd try and find out.

On the label that came with the canvases, it said "canvas stretcher bars", so I Googled it, and came up with a lot of stuff about making canvas, stretching your own canvas, and framing canvas, but nothing about my little wooden friends. It turns out stretcher bars are the actual lengths of wood that hold the canvas together. I should have known that! In a last ditch effort, I typed in "little pieces of wood that come with canvas", and Google threw up this page from painting.about.com. Apparently the little wedges are called canvas keys, and they're used to tighten a sagging canvas. Well, it just so happens, as I mentioned yesterday, that I'm currently suffering from sagging canvas syndrome, so I thought these would be just the ticket. The site says that "you put them into the slots made for them in the corners of the stretcher bars, then tap them in further to tighten or square up (align) the canvas." Well I put one in one of the slots made for them, and it went straight through and tried to poke through the canvas on the other side! I thought I must be doing something wrong, but I just couldn't get it to wedge in there. Then I tried it on one of the new canvases I got today, and it worked a treat. That's what you get for buying ultra-cheap Chinese canvas!

Anyway, I did another search for canvas keys but nothing much came up, so I'm not convinced that that is what they're really called (or maybe they're just too insignificant to have many web pages dedicated to them). If anyone can confirm or deny this, you would satisfy my curiosity. (I really should have more important things to think about!)

Tags: canvas, stretcher bars, canvas keys, canvas wedge, painting