Feeler gauge

How it works

Each blade carries its thickness in thousandths of an inch or hundredths of a millimeter. The user selects a blade and tries it in the gap; a blade that enters and a next-larger blade that does not bracket the size of the gap. Starrett’s 1902 catalog says that the blades may be used singly or in combination with others, so that any thickness in thousandths within their limits can be obtained quickly.

The tool measures by comparison with known thicknesses, not by reading a scale.

Anatomy

Blades (leaves): Thin hardened steel strips, each marked with its thickness. Draper’s data sheet describes hardened and polished taper blades.
Case with thumbscrew: The blades fold into a plated steel case held by a thumbscrew (Draper); Starrett’s 1902 catalog says its gauge’s leaves fold within the case.
Feeler stock: Bulk strip supplied in rolls or 12-inch lengths, cut to the needed length; Starrett sold it in 13 thicknesses in 1935.

Variants

Folding-blade set: Blades pivoted in a case. Draper lists a 10-blade inch set of 0.0015 to 0.025 inch with 100 mm blades, and an 18-blade combination set of eight metric and ten inch blades with 75 mm blades.
Feeler stock: Strip cut to length for long-reach or special work; Starrett says it is also useful for shimming in fixturing and die work.
Fixed railway feeler gauge: A single-purpose steel feeler gauge made at Crewe works for the London Midland and Scottish Railway, cataloged by the Science Museum Group as a feeler gauge, marked with its intended use.

Specifications

Blade thickness range, inch · in: 0.0015 to 0.025The range of Draper’s 10-blade set; Starrett’s 1935 feeler stock begins at 0.0015 inch.
Blade thickness range, metric · mm: 0.05 to 0.50The metric blades of Draper’s 18-blade combination set.
Blade length · mm: 75 to 100The blade lengths in Draper’s two sets.

Made to

DIN 2275
BS 957

Tips

Combine blades to reach an in-between thickness
Starrett’s 1902 catalog says its thickness gauge, or “feeler,” has leaves marked with their thickness in thousandths of an inch and that they can be used singly or in combination, so that any thickness within their limits can be obtained quickly.1
Cut feeler stock to the length the job needs
Starrett says its stock, supplied in bulk, can be cut to the required length for adjusting tappets, spark plugs and distributor points, checking bearing clearances and gear play, fitting pistons, rings and pins, and gauging narrow slots. It describes the bulk strip as ideal for long-reach jobs.1
Use the leaves to measure how far a surface is from a reference
In its instructions for a V-edge protractor used to check the alignment of motor cylinders, Starrett’s 1935 catalog says the variation between the protractor head and the face of the block is found with thickness or feeler leaves, and the reconditioning machine adjusted from it.1
Use the strip for shimming
Starrett says feeler stock is useful for shimming in fixturing and die work, in addition to measuring clearances.1

History

Earliest documented

about 1902 (earliest catalog evidence located)

Athol, Massachusetts, United States (L. S. Starrett Company)

Starrett’s Catalogue No. 17, dated 1902 by the Internet Archive, lists a “Thickness Gauge or ‘Feeler’” whose leaves are marked by thickness in thousandths of an inch, ranging from .001 to .025, and that may be used singly or in combination. This is the earliest dated evidence located for this entry, not the origin of the tool.1

The feeler gauge is a gap-measuring tool, and its history as far as it can be sourced is the history of its catalog descriptions. Starrett’s 1902 catalog already describes the “thickness gauge or ‘feeler’” with leaves marked in thousandths of an inch, used singly or in combination, so the form of a case of marked blades and the combining of blades were established by that date.

By 1935 the catalog presents feeler stock as an automotive tool. Starrett says it had become a necessity in that field, where an accurate fit gives quiet running, and lists setting valve tappets, ignition points, ring groove clearance, gear play, fitting pistons and adjusting spark gaps among its uses. The same catalog also uses the leaves in a measuring role beyond engines, to find the variation between a protractor head and the face of a cylinder block.

The modern forms are the folding-blade set and the stock. Draper’s data sheets show hardened, polished taper blades, each marked with its size, folding into a plated steel case, in inch, metric and combination sets. Starrett’s present product page treats the bulk strip as a separate product cut to length for tappets and other work. The earlier history is not sourced here, and what the feeler gauge displaced is not established by any source read.

Timeline

about 1902
Starrett lists a thickness gauge or “feeler” with leaves marked in thousandths of an inch, ranging from .001 to .025 inch, folding within a case.1
1915 (object number)
The Science Museum Group catalogs a set of steel feeler or thickness gauges with 10 blades, by J. Chesterman & Company of Sheffield, as object 1915-284.1
1935
Starrett’s Catalog No. 25 offers Feeler Stock No. 667 in 12-inch lengths in 13 thicknesses, beginning at .0015 inch. It says the stock has become a necessity in the automotive field, for setting valve tappets, ignition points, ring groove clearance, gear play, fitting pistons and adjusting spark gaps, and is used by toolmakers and machinists in experimental work.1
2003
Draper Tools’ data sheets list a 10-blade inch feeler gauge set of 0.0015 to 0.025 inch and an 18-blade combination set of eight metric and ten inch blades, each blade marked with its size and folding into a plated steel case with a thumbscrew.1 2
current
Starrett sells feeler or thickness gage stock for tappets, spark plugs, distributor points, bearing clearances, gear play, piston, ring and pin fitting, narrow slots and shimming.1

Gaps in the record (7)

No source read gives an inventor, date or place for the feeler gauge; the earliest evidence located is a Starrett catalog of about 1902.
The Science Museum Group’s record of the Chesterman set gives an object number beginning 1915 and a maker and place, but no made date; the 1915 in the timeline is the year in the object number, not a confirmed date of manufacture.
The timeline has five events rather than the six the brief asks for; the rest could not be sourced to the required standard.
The 1902 catalog scan is poorly OCR-recognized; the wording cited is limited to what could be read, and the number of leaves is not stated here for that reason.
No manufacturer instruction on how a blade should feel in the gap (drag), on stacking limits or on wear was located; forum posts that describe a go and no-go method were not used.
No standard text was read; the standards listed are candidates to be resolved.
Care and safety have no sourced entries.