Roger Clark Motorsport Extreme High Performance 11mm Head Stud KitThe RCM1540 Extreme 11mm Head Stud kit is an absolute must for your performance build. Manufactured from Aircraft Grade S99 Steel, and with a tensile strength in excess of 237,000 Psi (1640MPa), our 11mm kit reduces head movement under boost, and provides optimum head to block clamping, ably dealing with the higher combustion pressures associated with a modified performance engine, up to around 450Bhp.