Which instrument is typically used to verify a small clearance dimension such as spark plug gap?

Which instrument is typically used to verify a small clearance dimension such as spark plug gap?

• A. Feeler gauge
• B. Caliper
• C. Micrometer
• D. Ruler

Answer: (A)

The important idea is using a tool that can read very small, precise thicknesses. A feeler gauge is built for that purpose: it’s a set of thin blades, each with a known thickness. You pick the blade that just fits into the spark plug gap, or use a go/no-go blade to confirm tolerance. This directly gives you the clearance in thousandths of an inch or hundredths of a millimeter and lets you verify whether the gap matches the engine’s specification. Other tools like calipers or micrometers measure overall distances or dimensions, not the fine gap between two points in a small opening, and a ruler is far too imprecise for such a small clearance.

The important idea is using a tool that can read very small, precise thicknesses. A feeler gauge is built for that purpose: it’s a set of thin blades, each with a known thickness. You pick the blade that just fits into the spark plug gap, or use a go/no-go blade to confirm tolerance. This directly gives you the clearance in thousandths of an inch or hundredths of a millimeter and lets you verify whether the gap matches the engine’s specification. Other tools like calipers or micrometers measure overall distances or dimensions, not the fine gap between two points in a small opening, and a ruler is far too imprecise for such a small clearance.