APV60 - tclederman is right, most of them are welded. 3" spacing between spot welds. You could use bolts, every 6", but that's a lot of bolts. Usually only rear fenders or structural members were attached by bolts to bedsides.
However, the strips are usually attached to the bed floor with bolts at the same 6" spacing. You could use bolts, but the bolts in the corners and double bolts at 6" along an angle strip looks kind of funny.
P.S. There are no dumb questions here, just the silly mistakes we make for not asking.
