Bolts are installed by drilling a hole into the rock. Most modern bolts do not require glue. Instead, they expand in the hole when hammered in. Hangers are the pieces of metal that bolt to the wall. They have an opening that you can clip a quick draw to when rock climbing, or that you can thread webbing through to rig a rappel. Most bolts at the top of a rock climbing route have a length of chain, often about a foot long, attached to the hanger. After you're done climbing the route, you thread your rope through the bottom link of the chain and rappel down. Then when you pull your rope, you don't leave any personal gear on the wall.