thank you mate, yes that makes sense now!HB is front FH is rear, I think short for something like HuB and FreeHub
It will be FH-452 for mountain-Lx
FH-450 is Exage Mountain and would be for a 6speed setup and only up to 130mm.
Info for
si.shimano.com
si.shimano.com
Compare the lengths, and again early 90s Exage ###LX and Deore LX