The seat will have a "Y" bracket that holds the pivot as well as the springs, and then a nice fat clamp to go around the bike frame tubing underneath. This allows the whole seat assembly to slide up and down the tube to get it just where it suits you.
Originally Posted by marvin martian
Wow! Those are going to be the starting point for some awesome MBs! I can vouch for the comfort of the seat you are going to use. I have one on my bike and highly recommend it. I am planning to use the same seat on my next? build, a Jesse James Chopper. Will you make a sliding bracket for the rear springs of the seat to rest on also?