Which gauge is used to measure a hole diameter by reading the ball end of the gauge with a micrometer?

• A. Telescoping gauge
• B. Small hole gauge
• C. Inside micrometer
• D. Dial indicator

Answer: (B)

When you need to determine a hole’s diameter with a micrometer, use a tool designed to reach into the bore and present a size that the micrometer can read directly. The small hole gauge has a slender stem with a ball at the end; you insert it into the hole, adjust until the ball just fits and makes contact with the walls, then remove it and read the corresponding dimension with the micrometer. The ball end ensures smooth, even contact with the hole walls, reducing error from edge contact and corner geometry. This setup gives a direct hole size reading once the gauge is back on the micrometer. Other tools work differently: a telescoping gauge expands inside the hole and you measure its span with a micrometer; an inside micrometer measures internal dimensions directly with its own measuring faces; a dial indicator measures displacement rather than providing a hole diameter reading from a micrometer.