The headlight mounting hole is 3/8 inch

45” solo

6T Thunderbird etc

you don't want one sliding off while taking a corner or twisting the throttle

Recommended set-up is one magneto firing left plugs

Tear Drop Air Cleaner - Chrome - 1993-2009 Harley-Davidson Big Twin Brand_Cycle Standard The headlight mounting hole isThis kit allows you to use an iconic S&S Cycle Teardrop air cleaner with your stock Harley Davidson CV carburetor. The efficient, free flowing design can add two to five horsepower. A performance air cleaner is a must to get the most out of performance exhaust, cams, big bore or stroker kits. Kit includes aircleaner backplate, pleated, washable filter element, aluminum teardrop cover, all required hardware, and instructions. See Additional Information