Feeler gauges

Feeler gauges are measuring instruments for measuring the gaps, the interspace between two surfaces. These are flat metal strips of varying thicknesses. The thickness is marked on each sheet. They are delivered in sets of different sizes in millimeters or inches, usually in the range from 0.05 to 1 mm. Some kits contain measuring strips made of brass that are used to measure magnetic components. Brass is a non-magnetic material and the gap can be measured without any problems.

Feeler gauges

Feeler gauges are used to determine the clearances on bearings, pistons, valves, etc.

Some feeler gauges are bent (a) to make it easier to insert where space is tight. The others are stepped (b), ie the end of the leaf is of nominal thickness and the number is higher in the interior. Feeler gauges are not used to measure a spark plug gap because the surfaces of the electrodes are not perfectly parallel. Wire gauges (c) or special oval gauges are used for spark plugs.

Bent (a), stepped (b) and wire (c) feeler gauges

Before measuring the gap, check and remove dirt and rust from the measuring surfaces. Also, check that feeler gauges are not rusty and, if necessary, lightly lubricate them so that they glide more easily. Feeler gauges are never used to measure machines in operation. After measuring, wipe the feeler gauge set with an oily cloth to prevent rust.

One of the sheets is selected to measure the gap. If the feeler gauge feels too loose when measuring a gap, select the next size larger, and measure the gap again. Repeat this procedure until the feeler gauge has a slight drag between both parts. If the feeler gauge is too tight, select a smaller size until the feeler gauge fits properly.

If you do not have a feeler gauge to measure the desired thickness, you can connect two or more feeler gauges in the sum of which the required thickness is obtained. Also, when you want to measure an unknown gap, you can combine feeler gauges until their thickness fits into that space. By adding the thicknesses of all used feeler gauges, the size of the measured gap was obtained.