LB1 High Performance Precision Telescopic Bore Gauge Tool Set - 6 Pieces (5/16" to 6" Range) Precision Telescopic Bore Gauge Tool Set - 6 Pieces (5/16" to 6" Range) Professional Precision Tool Set! Easily Adjust with Twist Lock. Spherical Measuring Faces are Hardened. Polished Satin Chrome Finish, with Case Included. Range: 5/16 to 6 (8mm  150mm).