Adjustable Billet By-Pass Regulator 3/8 NPT Kit Adjustable Billet By-Pass Return Style Fuel Pressure Regulator 3/8 NPT Kit with Fuel Pressure Gauge and Adapter Fittings Boost Reference 11 HolleyHolley Billet Fuel Pressure Regulators are part of a complete line of fuel system products from Holley. They are precision machined from 6061 T6 billet aluminum for strength and durability. These regulators are adjustable from 4 65 psi and will handle both carbureted and EFI applications. A second pressure spring is included allowing you to increase the fuel pressure range up to 65 psi for EFI systems. They have 3 8 NPT port sizes to adapt to your new