The Hope RX4 Caliper Flat Mount is a drop bar compatible 4 piston calipers specially designed to work with Shimano or SRAM brake lever master cylinders, aimed for Road and Cyclocross use. Hope RX4 Caliper Flat Mount Features SHIMANO COMPATIBLE CALIPER RX4-SH caliper model designed to work solely with Shimano system, available in 3 version : Std Postmount Front Flat mount direct, fits directly with a Ø160mm rotor Rear Flat mount direct, fits directly with a Ø160mm rotor The RX4-SH caliper can replace the following Shimano caliper references : Flat mount : BR-R9170, BR-RS805, BR-RS405, BR-RS505 Postmount : BR-RS785, BR-R785 RX4-SH caliper will only work with mineral oil brake fluid SRAM COMPATIBLE CALIPER RX4-SR caliper model designed to work solely with SRAM system, available in 3 version : Std Postmount Front Flat mount direct, fits directly with a Ø160mm rotor Rear Flat mount direct, fits directly with a Ø160mm rotor The RX4-SR caliper can replace the following SRAM calipers : Force, Red and Rival RX4-SR caliper will only work with DOT4 or 5.1 brake fluid