These 5/8" bore master cylinders are manufactured from 6061 T-6 Billet Aluminum. The brake hose attaches to the inside front using a 3/8"-24, 10 mm banjo bolt. They have two 5/16"-18 threaded holes 2-1/8" apart for mounting. These are also a replacement master cylinders for all Accutronix Softail forward controls.