spool weight difference

For o.p's original question: I don't know for sure, but I'd guess that a spool weighs about a third of a clutch sg. Also about a third the cost, and maybe a sixth of a dapco locker or a trutrac.
I have a dapco (detroit) locker in my 8 3/4, a spool in one of my nines, and gonna put a slip-in locker in the open carrier in my other nine.
The narrower the tire, the better the spool works on the street. Dragging a 14"wide tire around a corner with a spool gets old.
(I would guess that an aluminum center with a spool would be about half the weight of an iron center with a clutch sg.)