Wilwood's GP310 Rear motorcycle disc brake caliper has been designed and engineered for use on 1984 - present Harley-Davidson Motorcycles. Built around a 4-piston, high performance powerhouse, this billet aluminum caliper brings distinctive, bolt-on styling: Bracket-mounted calipers with a standard 3.50" mount spacing are available for all most models (except Springer and 4-speed FL models).