'65 Formula S Tachometer Help?

The two studs on the back/rear of my tach are exactly the same length. However, they are different colors. Looking at the back of the tach, with the lamp at the 12 o'clock position, the stud on the left is brass colored and the stud on the right is steel colored.

The stud on the left also has a flat round washer on it colored brown. At first I thought it was a fiber type insulating type washer, but now I'm not sure because it actually feels like it is metal.

The stud on the right had no washer. Now I remember removing it and the tab for the wire connection, of course, was between the nut and the body of the tach, so I suppose a washer is not needed there. Unless, of course, it fell off sometime in the last 50 years.

I do have the update circuit board that is sold to repair/update the operation of the tach (still in the box somewhere, I will be searching for it). It will be exciting to bring this tach back to life.