Which instrument is recommended for measuring the inside width of a keyseat?

• A. Caliper depth gauge
• B. Dial caliper
• C. Tape measure
• D. Vernier depth gauge

Answer: (B)

Measuring the inside width of a keyseat requires a tool that can reach into the opening with opposite jaws and give a precise reading across the gap. A dial caliper is ideal because its internal jaws fit inside the seat and span the width, giving a direct, easy-to-read measurement on the dial. You bring the jaws together until they touch both walls, then read the dimension. Tools designed for depth—like depth gauges or depth-caliper variants—are meant to measure how deep a feature sits from a surface, not the width of a slot. A tape measure is too coarse for this small feature, and a vernier depth gauge also focuses on depth, not width. So the dial caliper is the proper instrument for this measurement.