Flat feeler gauges (see picture) are a set of plates of a certain thickness with the corresponding markings, used to measure various gaps. Also, flat feeler gauges can be used, for example, to measure axial play where the use of a dial indicator (see below) is difficult.
The set of flat feeler gauges must be protected from excessive force and impacts so that the feeler gauge plates are not bent or damaged. The surface of the flat feeler gauges must be kept clean and covered with a thin layer of oil to prevent corrosion.
When measuring the gap, it is necessary to select a flat feeler gauge that will fit with little resistance between the two parts. It is recommended to have two sets of flat feeler gauges to ensure measurement accuracy.