Floating (most common) - Usually one piston (sometimes two but side by side) and caliper slides in the bracket allowing both pads to contact the rotor.
Fixed - Caliper unit is bolted in place and have 2 or 4 pistons that oppose one another and provide force for both pads
Brake hose connects here - brass washer should not be reused.
"D seal rolls when pedal releases and pulls the piston back slightly to keep pads from being in direct contact with rotor.
