Replace Brake Pads on Mountain Bikes

"So now I'm going to move on to replacing the disc brake pads on the Avid disc brakes. One nice thing about the Avid brakes: they come with this little spacer that you stick between your pads when you take your front wheel off, or your rear wheel off. So if some uninformed friend decides to pull your brake lever a bunch of times, your pistons won't get pushed together. So it just sticks in there like that and you can see right now I don't have the pads in there. This is only effective when you have pads in. But you just stick the disc spacer in there. You can see it's marked for the rotation, which way the wheel rolls. So since this is mounted on here and the wheel rolls forward, rotation, the proper insertion direction is like that. You can see it fits in there, all cute, comes out the top. And now I'll show you how we're going to replace the pads."