Yes, we typically have an indent machined into the back side of a panel for the anti-rotation tab on thicker panels which are also structural. This presents 2 issues: The machine shop has to set up for the milling the indent, at extra cost, and there may not be sufficient thickness on a given...
This isn't it - you missed my point about it being an external star lockwasher.
I've used these "anti-twist" tab washers inverted with a plain internal star lockwasher between it and the panel. Torqued down tightly, the lockwasher will dig into the backside of the (preferably aluminum) panel...
I have a vague memory, from too many years ago to count, that many toggle switches came with a special lock washer. For the typical 1/2" dia. threaded bushing with a keyway, an external star lockwasher was provided with an internal tab to fit the keyway. This allowed the switch to be mounted in...
