I have heard of but not seen such a tool. It would have 2 sections
that rotate independently and are crescent shaped.
Two handles would protrude. Insert into the spar pin holes that have
been placed roughly into correct position so that you can see through
both, turn handles to 180 degrees apart aligning the holes, remove and
install your spar pin.
This would be a great help for one-man rigging. Does anyone know who
sells these or does anyone have a drawing of one? My pins are 30mm
diameter and 100mm long but a drawing could be changed for any size.