From Lowbrow Customs: Mount your solo seat easily with these weld-on solo seat spring mounts. Made of 1018 cold rolled steel for easy welding, they are 1 inch diameter with a 3/8 inch shaft for the spring to sit over. They are coped at 1 inch to fit standard size frame tubing, but can easily be enlarged to fit larger 1-1/4 inch tube if necessary. They come with a pair of 1/8 inch thick leather washers to keep your springs from squeaking, as well as two spring cotter pins to hold your springs in place on the cross-drilled shafts. Price is for a set of two mounts, spring cotter pins and leather washers. Made in Ohio, USA.
These are for mounting coil springs only, for hairpin style springs you want to use the Solo Seat Hairpin Spring Mounting Kit