Wilwood's GP310 motorcycle disc brake caliper has been designed and engineered for use on 1984 to 1999 Harley - Davidson Motorcycles. Built around a 4 - piston, high performance powerhouse, this billet aluminum caliper brings distinctive, bolt - on styling Direct leg - mounted calipers are available for all single and dual disc models (except Springer and 4 - speed FL models), as well as the 1983 XR 1000.