5/8-18 to 5/8-24 Thread. This quality precision made adapter allows you to convert your existing 5/8-18 threads to 5/8-24.This 5/8x18 to 5/8x24 adapter has wrench flats to ensure a tight fit. Black Oxide finish. Guaranteed to be concentric to your threads. For use with any threads of 5/8-18.