The third tier of the disc brakes parts diagram is the brake release unit. This unit fits into the hole in the middle of the brake housing. The bottom of the unit is the brake lining, the center is the packing and the securing piece is the brake release itself.
A disc brake parts diagram shows the brake assembly divided into three components. At the bottom is the brake disc. In the middle is the brake housing, which fits into the brake disc. On the right side of the housing is the bleeder adapter, which fits into the packing and is covered by the bleeder valve. This is held in place by a washer and screw. Moving clockwise on the housing finds the brake disc guide assembly.