These magnetic backs provide a quick and easy means of attaching any Starrett® AGD indicator to flat, ferrous metal surfaces. A real time saver for machine, jig and fixture set up. Requires no clamps, rods or snugs. A special 5/16"-24 threaded stud back is provided to replace the standard lug back. The powerful, permanent magnet is then attached to the threaded stud. Anti-magnetic indicators are not required. Magnetic Back for No. 655 Series The powerful, permanent magnet is then attached to the threaded stud. Anti-magnetic indicators are not required.