A caliper hanger is a simple heavy-duty wire hook used during brake work. When you remove a brake caliper to replace the pads or rotors, the caliper cannot be left hanging by its flexible rubber brake hose. Calipers are heavy cast-iron parts, and the brake hose is only meant to carry fluid under pressure, not hold weight. Letting the caliper hang puts extreme tension on the hose, causing internal cracks, leaks, or separating the hose from its metal end fittings.
The caliper hanger hooks through one of the mounting bolt holes on the caliper body, while the other end hooks onto a suspension coil spring, upper control arm, or frame member. This holds the caliper securely out of the way, keeping the brake lines safe from damage. You can make simple hangers using wire coat hangers, but professional steel hangers are stronger and won't bend or drop the caliper.