Which tool is used to measure the clearance between a surface plate and a relatively narrow surface being checked for flatness?

Which tool is used to measure the clearance between a surface plate and a relatively narrow surface being checked for flatness?

• A. Depth gauge
• B. Dial indicator
• C. Thickness gauge
• D. Micrometer

Answer: (C)

Measuring how far a surface is from a perfectly flat reference involves reading the actual gap between the surface plate and the surface being checked. For a relatively narrow surface, you want a tool that can fit into that small gap and give a direct thickness reading. A thickness gauge is designed for this purpose: it is used by placing the gauge between the surface plate and the narrow surface, and the reading shows the exact clearance. By taking readings at multiple points, you can assess whether the surface is within flatness tolerances. Other tools aren’t as direct for this task: a depth gauge measures depths in holes or slots, a micrometer provides a single thickness measurement of a part rather than a gap between two surfaces, and a dial indicator is excellent for sensing deviations in height across a surface but doesn’t give a direct gap measurement between the plate and the surface.

Measuring how far a surface is from a perfectly flat reference involves reading the actual gap between the surface plate and the surface being checked. For a relatively narrow surface, you want a tool that can fit into that small gap and give a direct thickness reading. A thickness gauge is designed for this purpose: it is used by placing the gauge between the surface plate and the narrow surface, and the reading shows the exact clearance. By taking readings at multiple points, you can assess whether the surface is within flatness tolerances. Other tools aren’t as direct for this task: a depth gauge measures depths in holes or slots, a micrometer provides a single thickness measurement of a part rather than a gap between two surfaces, and a dial indicator is excellent for sensing deviations in height across a surface but doesn’t give a direct gap measurement between the plate and the surface.