the bolt that holds the sidemount clamp together is special, and looks like it was a hand made low production item.  since I was missing one, I decided to make it.

Here is the bolt in question:

as you can see, it has a spring clip on it to retain it in the casting that holds the sidemount in place.  This is not a standard bolt.  Threads are 9/16-12, the max diameter is 1 inch, the hex head is 3/4 inch.

So, first we make the hex head, using a mill:

I use a hex shaped collet holder and a 1 inch collet.  Here is the result - my piece of bar scrap now has a proper 3/4 inch hex head on it.

Once the part is mounted in the lathe, a parting tool makes the groove for the wheel lock (sorry for the low grade photo).

Now, to turn the shank to the proper size - three diameters, the shoulder, the max diameter of the threads, and the very end that is the minor diameter of the threads.  The cross slide is set to a 30 degree angle to cut the tapered part.

Here is the finished part, in the casting that it holds in place.  This casting sandwiches the sidemounted spare to keep it from moving.