TC Bros. weld on chopper hardtail solo seat spring mounts. They are CNC Machined from 1018 cold rolled steel and are ready to weld on. Stud is 3/8" diameter and base is 1" diameter with a 1 1/8" radius coped into the mount. Easily fits 1" and 1 1/4" cross tubes as well. They also include a pair of hairpins, steel washers, and leather washers to keep your springs quiet and protect your paint. Just like our front seat pivot these are universal and can fit endless applications.