Modestly priced brand NEW Nissin master cylinders performs as good as the Big money brands.
Here's two sportier versions with different options so READ entire description.

For a single radial 4-piston or dual 2-piston Tokico calipers, the 16mm is it.

For Single 2-piston (stock FXR) or Single Tokico 2-piston Caliper (SK adapters for '99-down), The 14mm is it.

Set comes complete with ASV levers and include clutch side modified for stock HD Clutch cable. Amazing fit and pull. All stainless hardware included and black Goodrich Banjo bolt (M10x1.25) fits stock brake lines.

NOTE: DO NOT MIX DOT4 and DOT5 BRAKE FLUID. All kits recommended to be installed by a certified mechanic. If you are unsure about installation, Please seek help and do not risk your life.