Analog bore gauge
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All models operate on the proven principle of two diametrically opposed measuring points, one fixed and one moving, plus a spring-loaded centralising shoe.
To check the actual size of bore, the gauge must be set to size with a ring gauge or micrometer and inserted into the bore.
It is then necessary to 'rock' the gauge slowly to locate its measuring axis to the bore, shown by the point of reversal of the indicator hand or analogue display.
The reading at that point is the deviation from set or normal size.
For larger bores, a range of interchangeable extension rods allow a single instrument to cover a wide range of bore sizes.
