Generic 66390 Air Cleaner Stud Adapters 1/4-20 to 5/16-18, 2-Pack, 0.92in Corrosion-Resistant

These two precision-machined 66390 air cleaner stud adapters convert a 1/4"-20 wing-nut air cleaner stud into a 5/16"-18 carburetor mounting stud quickly and securely.

When you need to mount an air cleaner to a carburetor with mismatched thread sizes, the Generic 66390 adapter pair provides a simple retrofit without altering the air cleaner housing. Each adapter is 0.92" long, with a 1/4"-20 female thread on one end and a 5/16"-18 male thread on the other. Built from upgraded metal and precision-machined, these adapters resist rust and help maintain a firm seal between air cleaner and carburetor hardware.

How do these adapters fix thread mismatch problems?

They act as a threaded intermediary that accepts the original 1/4"-20 wing-nut stud while presenting the larger 5/16"-18 stud required by many carburetor mounting holes. Installation requires no modification of the air cleaner or carburetor—just screw the adapter onto the existing stud and then fit the carburetor mounting bolt.

• 1/4"-20 female thread mates with standard wing-nut studs.
• 5/16"-18 male thread fits common carburetor mounting holes.
• 0.92" length provides secure engagement without protruding excessively.
• Sold as a pair to convert both studs or keep a spare on hand.

Will these adapters affect the air cleaner's seal or performance?

Properly installed, the adapters maintain the original clamping force and do not change the air cleaner's geometry, so they should not compromise the seal or airflow. Precision machining ensures a snug fit to help prevent loosening and potential leaks during engine vibration.

• Exact thread dimensions reduce play and potential leaks.
• Corrosion-resistant metal keeps threads intact over time.
• Short length avoids interference with housing or intake components.

How durable are these adapters and what materials are used?

Each adapter is made from upgraded metal with corrosion resistance, offering longer service life than inexpensive, untreated fittings. Precision machining tightens tolerances so threads engage smoothly and remain reliable under normal engine vibrations and operating conditions.

• Upgraded metal resists rust compared with uncoated alternatives.
• Precision-cut threads reduce cross-threading risk during installation.
• Sold in a two-piece pack for immediate use on both studs or as a replacement pair.

How do I install these adapters safely and correctly?

Installation is straightforward: remove the wing nut or original stud, thread the adapter onto the 1/4"-20 stud, then secure the 5/16"-18 carburetor mounting bolt. Tighten to a firm hand/torque that secures the assembly without over-stressing the threads.

• Hand-start threads to avoid cross-threading.
• Use light torque—overtightening can damage stud or adapter.
• Check fit after initial run to ensure no loosening from vibration.

Who is this for: These Generic 66390 adapters are ideal for mechanics, restorers, hobbyists and DIYers who work on small engines, vintage cars, motorcycles, ATVs, or lawn equipment where carburetor and air cleaner thread sizes differ. If you want a quick, reversible, and durable way to adapt an existing 1/4"-20 air cleaner stud to a 5/16"-18 mounting hole without modifying parts, this two-pack delivers a practical solution.