Using feeler gauges correctly
Feeler gauges belong to the group of measuring gauges that are primarily used where measuring with other measuring devices is not possible or is awkward. You can use a feeler gauge to determine and specify the dimensions of gaps or other very narrowly cut spaces. The feeler gauge is also used to set various components (e.g. valve clearance, breaker gap, spark plug gap, etc.). A set of feeler gauges consists of gauge sheets of different thicknesses. The respective thickness of the blade is indicated in millimetres on the individual blades.
A distinction is made between conical and parallel feeler gauges (e.g. feeler gauge tape). In a conical feeler gauge, the gauge blade is pointed when viewed from above and has a rounded end (see picture). Parallel feeler gauges, on the other hand, run uniformly (parallel) to the rounded end.
Checking dimensions with a feeler gauge
Using the spark plug gap as an example, we will show you how to check a dimension. The optimum spark plug gap should be 0.7 mm (Fig. 1).
To determine the width or dimension, insert the thickest blade into the gap that still fits into it. The blade should slide "sucking". The next thicker blade should no longer fit into the gap or only fit with force (Fig. 2). The next smaller blade should wobble slightly or be easy to move.
The respective thickness of the blade - and therefore the width of the gap - can be read off the individual blades of the feeler gauge using the millimetre markings on them (Fig. 3).
Tips & tricks
- Bear in mind that the individual blades are not hardened and can therefore be damaged quickly.
- Lightly oil the blades after use to prevent rust.
- Make sure that the individual blades do not stick together unnoticed and thus impair the measurement (Fig. 1).
- Please note that worn or broken blades cannot be replaced. Feeler gauges are only available in sets.
- Fold the gauge blades into the housing to protect them when not in use (Fig. 2).
Tip
Our feeler gauge sets
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