Mechanical assemblies such as machines are built up from a series of mating parts. The fit of those parts is often designed to be within a specified tolerance that assures reliable operation for the machine – for example, the fit of a piston into the cylinder of an engine. If there is too tight a fit or clearance between the piston and cylinder, the engine may suffer from excessive wear and friction, shortening the life of the unit and resulting in maintenance costs and downtime. If the gap or clearance is too wide, combustion gases may escape during compression, reducing the engine performance. To make certain that gaps and clearances are within specified limits, engineers, mechanics, and machine operators rely on the use of measuring devices such as a feeler gauge.

What is a feeler gauge?
Feeler gauges, sometimes called thickness gauges or feeler gages, are mechanical measurement instruments that are used to provide a precise reading of the gap that exists between two parallel surfaces, such as the clearance between two machine parts or elements. Feeler gauges are typically sold as what is termed a set, with each set consisting of a series of dimensionally accurate pieces of shim stock that are joined using a common shaft and nut or riveted connection. The individual pieces, which are called blades, leaves, or plates, have very precisely calibrated thicknesses and can fold or fan out as needed when a measurement is to be taken, and can be recessed back on top of one another to fit into the gauge handle, which serves to protect the individual blades from damage when the tool is not in use. The blades are typically produced from a high carbon steel material. The use of high carbon steel is designed to ensure that the blade material will not compress during the measurement process, thus assuring that the gap measurements are accurate. Some models have a locking nut that can be tightened to maintain the blade position during use.

Each blade is annotated with its thickness designation. Different feeler gauge sets are sold with varying numbers of blades in them, which then corresponds to the overall gap range for which the gauge can be utilised.

Types of feeler gauges
The most common type of feeler gauge, called a straight leaf or straight blade gauge, consists of straight blades of uniform width constructed of high carbon steel sold in a set to cover specific dimensional values. However, there are variations on this standard that serve specific purposes.

Within the blade variety of gauge, some variations include changes to the blade length (long blade and short blade feeler gauges) as well as bent blade (also called offset) gauge sets. The bent blade gauge set can provide for easier use in space-constrained applications and for use in areas with restricted movement and access to the gap being measured. There is also a tapered blade type of gauge set, wherein the width of the blade becomes progressively narrower towards the blade tip, which again, can prove valuable when there are space limitations involved in the work area.

Go/no-go feeler gauges utilise blades that have a precision step between two specific thicknesses, rather than having blades that have a uniform thickness across their entire length. Go/no-go feeler gauges are designed to simplify the interpretation of the clearance or gap value by reducing the need to rely on the user’s “feel” of the gauge, instead bracketing the clearance or gap value with a greater than/less than tolerance window.

Another type of feeler gauge replaces the use of a shim stock type blade with calibrated metal wires whose ends are bent to a right-angle. This type of gauge is termed a wire feeler gauge or a spark plug gap feeler gauge, owing to its principal use for setting the gap on spark plugs for combustion engines.

While many feeler gauge sets are available as standard items for purchase, there are also suppliers who will create customised feeler gauges to meet specific needs or applications. These customisation options may involve providing gauges that feature alternative blade materials, packaging, blade sizes, blade shapes, and tapers, as well as specialised markings.

Hasberg offers strip steel in a wide range of forms and types
Hasberg’s product range includes strip steel in various lengths, widths as well as hardness grades. products made from strip steel (spring band steel, carbon steel etc.) in the form of feeler gauge bands and metal foils (for example, precision foils). Steel strip, such as carbon steel or spring band steel can be used in many fields of application.

For further details contact Duncan Macdonald & Co on TEL: 011 444 4345 or visit www.macduck.co.za