When the nut to secure the stud is fitted it should be tensioned up firmly, remembering that it is clamping down on fibre washers and a black insulator, so maximum crush should be avoided. Then the cable is connected, and the second nut run up. That second nut does need to be tight to make the best electrical connection. The thinned down wrench holds the terminal in place while the second nut locks the terminal tightly to the stud. There is no twisting/upsetting of the terminal bolt and subsequent damage to the starter.
The same applies to the generator terminal and the two terminals on the foot starter switch.
It is a special kind of hardened steel and I ground it down to make an excellent scriber. However, it has an even better use. When assembling T parts it is invaluable as an alignment tool for cotter pin holes. The fine tip can be used to first find the hole, and the nut can be turned a little to allow deeper penetration of the point to find better alignment of the hole.
What others are out there?
Allan from down under.
