Chrome-plated steel. Locking knurled handles and automatically self-centring plungers with constant spring tension for uniform contact pressure. Quick inside measuring of cylinder or hole bore by transferring dimension for external measurement. Indirect measurement by outside micrometer. Includes: 8 - 12.7, 12.7 - 19, 19 - 32, 32 - 54, 54 - 90 and 90 - 150mm gauges.