Friend has been given his grandfather's rigging knife. Is the pointed
tapered tool for untieing knots and opening the lay of a line called a fid?
What else is it for? On the side of the knife is a tapered slot routed
into the wooden handle and then overlain with steel with the matching slot
milled into it. The slot is not undercut . It is about 3/16" deep, about
1/4" wide at the large end and about 3/16 to 1/8" at the other. Whole slot
is about 1 1/2" long.

Is the slot another tool? What is it for?

Thanks,
Richard