BigKev wrote:
54 and prior didnt use the Hex style retainer bezel nut used in 55/56, but rather a bezel nut that is slotted on either side of hole. You use a small screwdriver on one side to work the nut around in the appropriate direction to tighten or loosen using a gentle tapping action.

But they do sell a tool that has a hollow interior to slip over the switch shaft, and engages the two slots. This makes things easier.