Editing Feeler gauge (section)

==Description==
They consist of a number of small lengths of steel of different thicknesses with measurements marked on each piece. They are flexible enough that, even if they are all on the same hinge, several can be stacked together to gauge intermediate values.  It is common to have two sets: one for [[imperial unit]]s (typically measured in [[Thou (length)|thousandths of an inch]]), and one for [[Metric system|metric]] (typically measured in hundredths of a [[millimetre]]) measurements (with intervals of thousandths of an inch and hundredths of a millimetre being roughly in the same order of magnitude).

The same device with wires of specific diameter instead of flat blades is used to set the gap in [[spark plugs]] to the correct size; this is done by increasing or decreasing the gap until the gauge of the correct size just fits inside the gap.<ref>{{cite book|title=Today's Technician: Automotive Engine Performance|first=Douglas|last=Vidler|first2=Don|last2=Knowles|page=36|isbn=978-0-7668-4864-1|edition=3rd, illustrated|publisher=Cengage Learning|year=2003}}</ref>

The lengths of steel are sometimes called ''leaves'' or ''blades'', although they have no sharp edge.

Stainless steel is a common material for feeler gauges. Some feeler gauge sets have a single blade of brass due to the historical reason that early electronic ignition systems required the air gap between the reluctor and the pickup part being set with a non-ferrous metal.{{cn|date=February 2024}}