55-57 Chevrolet Belair Wilwood Polished Master Cylinder and Black Powder Coated 7" 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.