Hy jimbo 24, if you are talking about the two bolts at the outboard end of the leaf spring brackets which appear to have only nuts on them but no heads on the other end, then those are the lock bolts for the shackle/leaf spring pins. Those pins are only threaded on one end and have no heads, they interlock into milled slots in the spring pins, they themselves have a taper milled onto them, you tighten the nuts to lock the pins to the spring pins, hope that helps.
