AG Mechanics CDE Practice Exam 2026 – The Comprehensive All-in-One Guide for Success

When measuring the spark plug gap, it is essential to use a wire or round feeler gauge. This type of gauge is specifically designed for measuring small gaps accurately, making it the ideal tool for checking and adjusting the gap on a spark plug.

A micrometer is typically used for precise measurements of larger objects and would not be suitable for measuring the small gap on a spark plug. A ruler or tape measure are designed for measuring lengths and are not precise enough for measuring the small gap on a spark plug.

Therefore, the correct tool to use when measuring the spark plug gap is a wire or round feeler gauge.