Which instrument arrangement is used to measure the inside diameter of a cylinder?

• A. Telescoping gauge and micrometer caliper
• B. Vernier caliper
• C. Micrometer only
• D. Dial bore gauge

Answer: (D)

Measuring the inside diameter requires an instrument that can reach into the bore and give a direct reading of size. A dial bore gauge is designed for this task: you insert it into the bore, the contact heads expand to touch the bore walls, and the dial indicator shows the diameter as you read it. Calibration is typically done against a micrometer set to the nominal size so the dial indicates the actual bore size with good accuracy and repeatability. This arrangement is preferred because it provides a direct bore measurement with high precision, unlike a telescoping gauge with a micrometer (which requires transferring the measurement between tools), a vernier caliper (less precise for bores), or a micrometer alone (which cannot access the interior of a bore).