Inside the caliper bracket, the brake pads do not sit against bare metal - they ride in small stamped-steel clips called abutment clips or pad slides. They are a small part with a big effect on how the brakes feel and sound. Here is what they do.
What they are
Abutment clips are thin metal clips that snap into the caliper bracket where the pad ears rest - see brake hardware clips. They give the pad a smooth, slightly springy surface to slide against as it moves in and out with braking and pad wear.
Why they matter
Good clips let the pad slide freely and stay lightly tensioned, which prevents rattle and keeps the pad from binding. Corroded or missing clips are a leading cause of brake noise and dragging pads; see why brakes squeak. Rust under a clip can also stop a new pad from fitting; see new pad won't fit.
Replace them with pads
Because they take constant movement and heat, abutment clips should be replaced with each pad change rather than reused - they usually come in the pad box. Clean the bracket seats and grease the slide points lightly, not the pad face; see brake grease points.
Bottom line
Abutment clips are cheap but critical for quiet, free-moving brakes. Fit fresh clips from a hardware kit whenever you install new pads.