A friend recently bought a 66 Hardtop to be used as a daily driver. This is what he found used as a battery clamp. The "technical" aspects are (at least the ones that are easy to figure out) as follows: the bolt is metric, a grade 9.9, 8X0.125X62 all millimeters; the "nut" looks like one used on fenders; the block is anyone's guess.
I will put this valuable artifact in with the rest of the junk treasures I've recovered.
Jim
PS, the quarter is for size reference (it was the first thing I grabbed).