This replacement spigot threaded screw is a converter stud that features a 1/4" thread on one side and a 3/8" thread on the other. It's a standard 5/8" size and is an accessory as part of equipment for studio lighting stands such as tripods, c-stands, studio light heads etc.. It's reversible with one side featuring a 3/8" screw and the other a 1/4" screw.