The knurled body is made of aluminum, and the central steel shaft is held in place by a spring steel locking plate which slips into the slots turned on the shaft. By releasing the locking plate, you can move the shaft in or out in either 3/8" or 1/8" increments. The only marking on the tool is a stamped "Australia."
It's clearly meant to act something like a depth gauge, but for what? I hope I don't hear from any Kangaroo proctologists.