If it is necessary to accurately measure the diameter of a hole approximately 1/4 inch in diameter, which gauge should be used?

If it is necessary to accurately measure the diameter of a hole approximately 1/4 inch in diameter, which gauge should be used?

• A. Telescoping gauge and determine the size of the hole by taking a micrometer reading of the adjustable end
• B. Small hole gauge and determine the size of the hole by taking a micrometer reading of the ball end
• C. Inside micrometer and read directly from the micrometer
• D. Plug gauge

Answer: (B)

When measuring a small internal diameter, the most reliable approach is to use a gauge designed specifically for small holes and then read the size with a micrometer. A small hole gauge with a ball end is ideal because you can insert it into the hole, expand it until the ball end just contacts the hole walls, lock it, and then measure the gauge with a micrometer. The ball end provides consistent, centered contact, reducing errors from edge interference and giving a precise size for about a quarter inch. Other methods have downsides for this size. A telescoping gauge requires transferring the measurement to a micrometer and can be less precise for small holes due to alignment and end play. An inside micrometer can read directly but may be hard to fit into a small hole or keep coaxial alignment. A plug gauge only indicates whether the hole is within tolerance, not the actual diameter, so it doesn’t yield the exact measurement needed.

When measuring a small internal diameter, the most reliable approach is to use a gauge designed specifically for small holes and then read the size with a micrometer. A small hole gauge with a ball end is ideal because you can insert it into the hole, expand it until the ball end just contacts the hole walls, lock it, and then measure the gauge with a micrometer. The ball end provides consistent, centered contact, reducing errors from edge interference and giving a precise size for about a quarter inch.

Other methods have downsides for this size. A telescoping gauge requires transferring the measurement to a micrometer and can be less precise for small holes due to alignment and end play. An inside micrometer can read directly but may be hard to fit into a small hole or keep coaxial alignment. A plug gauge only indicates whether the hole is within tolerance, not the actual diameter, so it doesn’t yield the exact measurement needed.