A common inspection instrument used to visually inspect internal bore surfaces is the

• A. Magnifying glass
• B. Phototube
• C. Microscope
• D. Borescope

Answer: (D)

Inspecting internal bore surfaces requires an instrument that can be inserted into narrow cavities and provide a clear view with illumination. A borescope fits this purpose: it's an optical probe with built-in lighting, available in rigid or flexible forms, often connected to an eyepiece or video camera to convey the image from inside the bore to the inspector. This allows you to check for surface defects such as wear, scratches, pits, or corrosion without disassembly. In contrast, a magnifying glass cannot reach inside a bore, a microscope is for bench-top close-ups of prepared samples, and a phototube is not used for viewing interiors. Therefore, the borescope is the standard tool for visually inspecting internal bore surfaces.