Used to check drywall fit around outlet boxes. Handle to hold it, pins to center it on the box in same orientation that the switch screws would put it in.
Cover to make sure no gaps showing.
Winner Winner Chicken Dinner!
Except I use it for device boxes in masonry walls, mostly. It seems to be getting harder and harder for masons to get cuts right, but once they see a guy checking every one, they quickly realize they need to do it right. I don't really know if I invented this, but I've never seen one before. The pins are just pop rivets that are just snug enough to still move, and the tail not sheared off (that takes a light touch LOL) and the center drilled and tapped to 8-32 which is the common drawer pull thread.