Straight Fuel Line

The Holley Straight Fuel Line adapter (HLY34-21) is a precision fuel system fitting engineered for hot rodders, engine builders, and performance mechanics who demand reliability in high-flow fuel delivery applications. This straight adapter bridges two critical fuel line standards—the 5/8-18 inverted flare connection on fuel pumps and carburetors with the 3/8-inch hose barb inlet on rubber fuel lines—eliminating kinks and flow restrictions that plague poorly matched connections. Whether you're converting a carburetor fuel system, upgrading to a modern fuel pump, or fabricating a custom fuel delivery setup, this Holley fitting ensures leak-free operation under sustained pressure.

Constructed from solid steel with a protective chrome finish, the Holley Straight Fuel Line adapter resists corrosion while maintaining the structural integrity required for fuel system duty. The 5/8-18 inverted flare male thread seats securely into factory and aftermarket carburetor inlets and fuel pump outputs, creating a mechanical seal that won't weep under idle or full-throttle conditions. The 3/8-inch hose barb outlet provides a secure grip on reinforced fuel line, preventing accidental disconnection during engine vibration or thermal cycling. Straight geometry—opposed to 90-degree elbows—minimizes turbulence and pressure drop, critical factors when running high-volume fuel pumps or gravity-feed systems on vintage platforms.

This Holley adapter is essential for classic car restoration, street rod builds, and vintage muscle car fuel system retrofits where original equipment no longer exists or modern standards apply. Mechanics and fabricators rely on it when converting mechanical fuel pumps to electric systems, adapting carburetors between different platforms, or restoring original fuel delivery integrity after years of corrosion. The compact 5 x 2.1 x 7-inch footprint integrates seamlessly into tight engine bays without requiring extensive rerouting. Installation requires no tools beyond a wrench for the inverted flare connection; simply slide reinforced 3/8-inch fuel line over the hose barb, secure with a hose clamp, and pressure-test to verify seal integrity. Compatible with all standard fuel line materials—cloth, rubber, and nylon—this Holley fitting delivers decades of dependable service in street, strip, and show applications.