This beautifully made gauge features dial-in micro adjustability for fabulously easy precision setting. Every detail has been attended to with care. The file hard (Rc60) marking blade is round, but it doesn't rotate during use; it slices with or across the grain as cleanly as a knife. The lockable brass head and tail, fitted with spring-loaded locking screws and a nylon tension screw as well, slice along a groove milled in the beam to keep them from rotating during micro-adjustment. The stout knurled brass adjustment nut is 1" wide for easy fingertip access. The head, 1-5/8" in diameter, is fitted with a countersink that houses the blade safely out of harm's way when not in use. It's a lovely tool, and beautifully functional, too.