Replace Brake Pads on Mountain Bikes

"So what I'm going to do is I'm going to make sure that when I'm inserting these, the holes - little reliefs in the back of my pad - line up with the pistons. So you can see how the pistons are in there, and it looks like this is the proper way to put them in, but it's not. So I'm going to start off by pushing the pistons back into the bore, which with the Hayes brakes, the appropriate wrench to use to do that is the open end of a 10 millimeter box wrench. You can see right there, it says "10mm." And why you need to do that is because these brakes are what's called a "closed hydraulic system." So as your brake pads wear, these pistons come out progressively farther to keep the throw that you have from your lever to the handlebar at a consistent distance. So basically, I'm just going there, push that back, push that other one back. It gives me more room to work with and the appropriate starting distance on these things for my new brake pads. So now I'm going to insert them one at a time or both at the same if you have space. And you want to hear them click, so it looks like I'm putting them in the wrong way. Nice, positive click. See everything is there, doesn't want to flop around. And the other positive click there. Nice, positive feeling. If it doesn't feel right, it's not right."