Analogue micrometers give the size on a scale, while digital micrometers show it as a number and can send readings by cable or wirelessly. Microtest makes both types of internal micrometer.

There are nine: 30–40, 40–60, 60–90, 90–140, 140–240, 240–400, 400–650, 650–900 and 900–1150 mm.

Extensions can be combined to reach 10 metres or more, so the same instrument can be used well beyond the length of a standard probe.

There is no single answer, because it depends on the bore diameter and whether you prefer reading a scale or a numeric display. Microtest lists analog, digital, Gold Edition and modular models, and its internal range uses the three-spindle system with repeatability of ±1–2 µm up to Ø400 mm.

The Microtest system compensates for temperature-related expansion errors, with 20 °C as the nominal reference. The contact points are insulated to limit heat transfer from the user’s hand.

They are used wherever bore diameters have to be checked against a drawing tolerance, in machining, production and inspection work.

Microtest lists its address in the Sharjah Free Zone, UAE, and buyers in Saudi Arabia can send enquiries through its website. For anyone comparing a micrometer supplier, the analog range covers bore sizes from 30 mm to 1150 mm.