Designed to be used in systems with a return line back to tank, It is adjustable from 4.5-9 psi for precise fuel pressure adjustments, Comparable and interchangeable with popular Holley® 12-803BP regulator, Features one 3/8″ NPT inlet, one 3/8″ NPT outlet and one 3/8 NPT return (or bypass), Constructed of billet aluminum with a black anodized base and clear anodize top for good looks. Holley 12-841 HP Billet Carbureted By-Pass Fuel Pressure Regulator. Holley® 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. They feature a black bright dip anodized body and a clear bright dip anodized top for corrosion resistance and good looks. The Holley 12-841 fuel pressure regulator features 3/8 NPT in/out ports and a 3/8 NPT return port. Adjustable from 4.5-9 psi for precise fuel pressure adjustments. Constructed of billet aluminum with a black anodized base and clear anodize top for good looks. Used in systems with a return line back to tank. Use with electric pumps only. One 3/8″ NPT inlet, one 3/8″ NPT outlet and one 3/8 NPT return (or bypass). 1/8 NPT gauge port. Comparable and interchangeable with popular Holley® 12-803BP regulator. Pressure Regulator Inlet Size. Pressure Regulator Outlet Size. By Derek on May 10, 2020. Very nice regulator for the price. Only problem is tightening fittings. There is no where to place a wrench on the body of the regulator. You need to use a vice, or pipe wrench which works but scratches the paint. But over all, very well built and does its job well. Yes, I recommend this product. By waydo on October 25, 2018. I used this for a carb swap on a tbi 89 firebird, worked great to meter down the fuel pressure right out of the box. Quality is good, comes with instructions and mounting hardware. Related Items / Suggested Parts. Holley 12-823 Regulator Rebuild Kit. Speedway Motors is America’s Oldest Speed Shop® and has been a trusted source for specialty rodding and racing products and friendly expert advice for more than 73 years.