HOOAI New Hammer Head 80T Trail Master MID 6.000.305 XRS XRX Go Kart Brake Master Cylinder Hammerhead part#: 6.000.305 HOOAI Hydraulic Brake Master Cylinder w/ Reservoir Assembly This master cylinder has one port for the rear brake caliper. Overall length of the base : 4 1/4" the mounting bolts spacing : 1 3/4". We are professional auto parts seller! Please feel free to contact us if you are not sure which part to order! Please cross-check before ordering, to make sure this is the right part you need!