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Glossary Index


Glossary Entries

Engineering Tools

Engineering Tools

Engineers working in metal use a wide variety of tools for measurement and marking out.

Components are measured either to establish their actual dimensions (direct measurement) or to compare them against a standard dimension (comparative measure). Micrometers, vernier calipers and dial indicators are used to take direct measurements while comparative measurements can be taken using radius gauges, screw pitch gauges and engineers squares.

Transfer measurement is a variation of comparative measurement where a dimension is first taken using for example a pair of spring calipers. The distance between the jaws of the calipers can then be read off using the graduations on a steel rule.

When selecting a tool the main consideration is the degree of accuracy, or resolution, required. While steel rules are generally accurate to 0.5mm (0.01in), standard micrometers are accurate to 0.01mm (0.0005in). Greater accuracy can be achieved using a micrometer with a vernier sleeve which is accurate to 0.002mm (0.0001in).

Given the accuracy of measuring tools, care should be taken to keep the workpiece and measuring faces clean and dust free. Highly ground workpieces should be held in some form of soft chamois-type cloth to reduce the effect of body temperature and protect the work from the effect of the natural acidity in the fingers which can mark and stain.

Precision tools should never be left lying on a bench or machine bed since they can so easily be knocked onto the floor and damaged. Keep them in the box in which they were supplied as this will help keep them clean and free from dust and grease. Micrometers should always be set by the use of setting gauges in order to adjust a 'true zero' before use.


Firm Joint

These are adjusted by pulling open or squeezing narrower by hand.


These are for taking internal comparative and transfer measurements.


These are for taking, transferring and marking out a set measurement, the straight leg acting as the datum basis and the bent leg and scraper point marking the work.


These are for taking external comparative and transfer measurements.


These are adjusted by a knurled nut for easier and finer adjustment.

Carbide Tipped

This refers to carbide tips on the measuring surfaces of a micrometer in order to prevent them from being worn in use.

Case Hardened

This refers to items which are hardened on the outside by the use of some form of compound. Hardened refers to items which have been hardened to a greater depth usually through the use of a furnace.


The collett is a circular sleeve which, when compressed, acts as holding clamp insert. Colletts are very often 'split' in the form of channels removed from the side in order to provide more elasticity and flexibility.


Dividers are used for marking out circles and taking transfer measurements from a template to the new work.

Feeler Gauges

These are used for gauging by feel or touch, the gap between components such as bearings or electrical contacts.


This refers to the process of very fine precision finishing when the product is rubbed with a very soft lapping compound across a surface table or other known flat face.

Lightly Tempered

This means that an item has been tempered but only a very little. While it may tend to be more brittle than an item which has been fully tempered, it has a sharper hardness.

Pearl Chrome Finish

This is sometimes called satin chrome. The rustproof finish designed not only to protect the tool against rust but also to provide improved reading without glare.

Radius Gauges

These are used for checking both internal and external radii.

Ratchet Mechanism

The ratchet mechanism is for ensuring that a constant pressure is applied to the product and that an incorrect reading is not taken by either over tightening or under tightening. The ratchet mechanism is designed so that the ratchet will slip when the correct pressure is applied (as in a torque wrench).

Screw Pitch Gauges

These are used to measure internal or external screw threads by selecting a blade which fits the existing thread.


The engineers precision square has a steel stock and a steel blade which should be ground and polished for extreme accuracy.

Engineers squares are used by some carpenters requiring extreme accuracy.

Stepped Jaws

These are in the form of a taper from outside to inside, but in a series of steps instead of a gradual taper.


This refers to a quenching process in order to remove the brittleness from a hardened product.

Thimble Mechanism

This refers to a similar feature as a ratchet mechanism but achieved through the thimble.

Vernier Scale

The scale provides a simple way of resolving more accurately a measurement reading which falls 'partway' between 2 discrete scale divisions.

A secondary scale, subdivided into 9 equal portions, is matched against a marker to register one further significant figure, eg. 2.06+ might be resolved to 2.063. Named after Jacques Vernier the inventor of the Vernier system.