The Starrett SA 711. Internal Measuring Machine Jaws is double-ended, self proving-assures parallelism and squareness. Designed for use with square style gage blocks, jaws are made of hardened steel 50.8mm long, 25.4mm wide and 12mm thick. Both side edges are lapped 90 degree square to the gaging faces within 30 seconds of arc and extend beyond the gage blocks in the combination, thus forming a square master. Jaw and gage combination parallelism is checked merely by turning the combination to the opposite side and rechecking the reading. Furnished in pairs.