Performance Machine Four-Piston Differential-Bore Rear Calipers For Harley Softail Features: Direct bolt-on calipers are machined from a single piece of billet aluminum As the name implies, they are ready to bolt on in one piece, instead of using the more common bracket and caliper design The brake calipers are designed for 11.5 disc application and utilize the 1.37 x 4B caliper