Keith Black Dome Top Piston Kit For Harley 74 FL / FX 1941-1979 Keith Black Dome Top Piston Kit are manufactured from high-strength, T-5, heat-treated, 390 hypereutectic aluminum alloy Features: Allow a tighter fit and longer piston and ring life Diamond-machined pistons are held to plus or minus one gram weight and less than one-half-thousandth inch (.0005) tolerances from piston to piston Each kit contains two pistons, pins, spiral-lock pin clips and Hastings moly rings Replacement piston rings and pin lock rings available separately Compression Ratio: 9.0:1 Piston Material: T-5, heat-treated, 390 hypereutectic aluminum alloy Note: KB pistons can be installed tighter than other pistons. This results in less piston rock and better ring seal. Please read instructions included with piston for correct piston clearance. Note: Due to the thermal conductivity and design of KB pistons, special attention is required to the top ring end gap. Please read instructions furnished with piston for correct ring installation.