55-57 Chevrolet Wilwood Polished Master Cylinder and Chrome 8" Dual Diaphragm Brake Booster with Brackets. This master cylinder features Polished aluminum finish with black anodized machined aluminum top. Master cylinder has a 1" bore and includes ports on both sides to work with all applications. Master cylinder outlets are 1/2-20 UNF and come with adapter fitting for 3/8-24 and 9/16-20. Master cylinder works with both disk/drum or disk/disk applications just change proportioning valve to match your set up. Kit also includes a dual diaphragm booster and is a great upgrade from a single diaphragm booster. Dual diaphragm boosters offer 19% better stopping over single. This is a safe and inexpensive way to upgrade both the safety and look of your ride.