What instrument is used to measure wear inside an engine cylinder?

• A. Vernier caliper
• B. Dial-bore gauge
• C. Dial indicator
• D. Depth micrometer

Answer: (B)

Measuring wear inside a cylinder relies on an instrument that can read the actual internal diameter accurately at several depths and around the bore. The dial-bore gauge is designed for this purpose. It slides into the cylinder and uses a contact head and a dial indicator to show the bore’s diameter as you move the gauge along the bore. By zeroing the gauge on a reference size and then taking readings at top, middle, bottom, and in different rotational positions, you can detect wear, taper, and out‑of‑round conditions. Comparing these measurements to the cylinder’s nominal size tells you how much material has been worn away and whether the bore is still within specification.

Other tools aren’t as suitable for directly measuring bore wear: a vernier caliper can measure inside diameters but isn’t practical for deep, precise measurements inside a smooth bore; a dial indicator measures small linear movement rather than a true diameter; and a depth micrometer measures depth, not the bore’s cross‑section.