A feeler gauge is a tool that is used to measure the distance or gap between two objects. Feeler gauges are used extensively throughout a variety of industries, to set up manufacturing equipment to ensure effective performance. They are also commonly employed for automotive engine components that require precise spacing in order to operate properly.
Feeler gauges are available in a wide range of English and metric sizes. A feeler gauge is usually purchased as part of a set that conatins a series of individual gauges with progressively increasing thicknesses. Gauges can also be purchased individually, and may be manufactured in custom shapes and sizes.
To measure the space between two objects, a gauge with a thickness that is close to the gap distance is employed first. If this gauge is too large to fit, the gauge with the next, lower thickness is used. If the gauge has excessive clearance, the feeler with the next, higher thickness is tried. This process is repeated, until a gauge that fits snugly in the gap is identified. The thickness of this gauge then represents the distance of the gap.
A flat feeler gauge, or blade, is typically one-half inch (1.27 cm) wide by several inches (or centimeters) long. A set generally includes a holder that contains a series of blades with different thicknesses. The blades fan out of the holder to allow the user to select the blade thickness of choice, and then fold the unused gauges back into the holder. Each blade is stamped with its thickness for easy identification. A flat feeler gauge is usually flexible, and can be bent for use in hard-to-reach places.
A wire feeler gauge typically consists of a holder that contains a series of round wires with different thicknesses. The wires are usually bent into a “U” shape, attached, rigidly, to the holder, and are less flexible than flat feeler gauges. Wire feeler gauges are frequently used in automotive applications for measurement of the spark plug electrode gaps, and other critical ignition clearances, such as valves.
A ramp or graduated feeler gauge increases in thickness along its length. There are markings that identify the thickness at multiple locations along the gauge. It is placed in the gap being measured, until it has zero clearance. The thickness of the gauge at this location represents the gap distance.
Feeler gauges are most commonly made of high-quality carbon steel, and are machined to a very smooth surface finish. Other blade materials are available, including stainless steel, brass, and plastic. Metal blades have better wear resistance and will maintain their accuracy after many uses.