Wilwood's Pro Street Series Fixed Mount Rotor Hats have a long standing reputation for fit, performance, and durability. HD Series hats are manufactured from premium grade aluminum alloys offering high strength, low weight, and show quality appeal. HD hats have not only been a mainstay in many of Wilwood's racing disc brake conversion kits, but they can cover a range of applications from an OE four lug axle shaft to a Grand-National stock car racing hub.