Open-ended caliper piston for automotive brake calipers: a hollow machined cylinder with an open bore. Under hydraulic pressure in the caliper, the piston pushes the brake pad onto the disc. The pistons differ in wall thickness and bore: a thin-walled sleeve in a bright metallic finish, a glossy black piece with a thick end face and a smaller bore, and a smaller bright silver piece with a stepped inner bore. They come from a brake range engineered to reduce noise and increase durability, alongside master pistons and hydraulic components. Materials offered: aluminium, brass, SS, MS and plastic.