# Mechanical Engineering INSTRUMENTS & GAUGES Terms and Definitions | Terminology | Meanings

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## Mechanical Engineering INSTRUMENTS & GAUGES Terms and Definitions :-

ACME THREAD GAUGE – A gauge used for checking and testing the 29° angle and the width at the end of a thread cutting tool while grinding it. It is also used for setting the tool square with the axis of the workpiece.

ANGLE PLATES – Some work has to be set at a particular angle to the surface of the table, and this is often effected by bolting it to an adjustable angle plate.

ARDOMETER – A type of total radiation pyrometer.

BORING BAR MICROMETER – On boring operations, it is often necessary to adjust the cutter setting by a few thousandths of an inch. With this, it is possible to determine exactly the depth of cut taken.

CALIPER – Instrument used for measuring distances between or over surfaces, or for comparing dimensions of workpiece with such standards as plug gauges, graduated rules etc.

CENTRE SQUARE – is intended for marking the centres of round or square stock.

CLINOMETER – Instrument used for measuring angles relative to the horizontal plane.

DEPTH GAUGE – Gauge used for the purpose of measuring the distance between two surfaces, to find or check the depth of a counterbored hole, a recess etc.

DIAL GAUGE – Instrument indicating the movement of a projecting plunger by the movement of a hand or pointer over a graduated dial.

DIAL SHEET GAUGE – Gauge fitted with a dial or clock for measuring or comparing the thickness of sheet metal plates.

DIVIDERS – These are essentially scribers for marking arcs, and circles, hence their points are hard and sharp. They are used for dividing distances into a number of equal parts. Also used for transferring dimensions from a rule to the work.

DRILL GAUGE – Tool for measuring the size of drills.

DRILL GRINDING GAUGE – A tool for checking the angle and length of the cutting lips on a twist drill while grinding it. Also it may be called a drill point gauge or a drill angle gauge.

ENGINEERS TAPERS – are intended for measuring hole sizes, slot widths, caliper settings and so on.

FEELER GAUGES – Consist of a number of thin metal blades, each of a different thickness and in the desired number of dimensional steps. They are used for checking clearances.

FIRTHS HARDOMETER – Instrument for measuring the hardness of materials, particularly metals.

GAUGE – A tool or instrument for checking or measuring the sizes of metal parts to determine whether the dimensions are within the specified limits.

GAUGE BLOCKS – are used mostly for reference in setting gauges and for accurate measurement in tool, gauge, and die manufacture.

HEIGHT GAUGE – Marking out or measuring tool designed on the lines of a scribing block, but capable of more accurate duty.

HERMOPHRODITE CALIPER – A caliper having one leg similar to that of an inside caliper, while the other leg is pointed like a divider leg.

HOOK RULE – A steel rule with a projecting piece or hook at one end at right angles to the edge of the rule.

INDICATING INSTRUMENTS – The instruments that provide visual observation of readings, such as pressure gauges, draft gauges, fuel oil meters and thermometers for fuel, feed water and flue gas temperatures etc.

INDICATOR – A sensitive instrument which shows slight variations when testing the trueness, or alignment of a workpiece, fixture or machine part such as a milling vice. Dial indicators may be graduated to read small linear variations.

INSIDE VERNIER CALIPER – is intended mainly for checking internal dimensions, such as the diameter of bores, and so on. Vernier protractor is used for measuring angles accurately.

JO BLOCKS – These refer to Johansson precision gauge blocks.

KNIFE EDGE VERNIER CALIPER – has jaws which are reduced to a very narrow edge. These are useful for measuring in restricted places or on curved surfaces.

LEVEL, HYDROSTATIC – U tube device employed during the levelling and setting of work too long for the use of a spirit level.

LEVEL, SPIRIT – Instrument consisting essentially of a small sealed glass tube containing spirit (alcohol or ether) so mounted that the enclosed bubble of air occupies a central position only when the instrument is placed horizontally.

LIMIT GAUGE – A gauge that represents a limiting (maximum and minimum) size within which the work will be acceptable.

MICROMETER – A precision, screw adjusted measuring instrument with which dimensions can be read in thousandths and ten thousandths of an inch.

MICROMETER COLLAR – A dial on the screw of a machine to indicate the extent of the movement of the screw or parts attached to the screw and usually graduated to read thousandths of an inch.

MICROMETER DEPTH GAUGE – The ordinary depth gauge has been

MINNIMETER – Delicate form of indicator showing the movement of a projecting plunger usually placed at one end.

ODD LEG – Caliper having one leg bent inwards at its ends, like the two legs on a pair of inside calipers, the other leg being pointed or having a separate hardened point attached to it.

OPTICAL FLAT – Plate generally made of glass or quartz and used as a standard of reference as a flat surface.

OPTICAL PROTRACTOR – Angle measuring instrument fitted with a scale read by an optical magnifying device.

PARALLEL BLOCK – Steel or cast iron block used when setting up work for machining, marking out or measuring.

PIN GAUGES – End measuring pins for determining bore diameters.

PLUG GAUGE – A gauge on which the outside measuring surfaces are designed to test the specified dimensions of holes. May be straight or tapered, plain or threaded, and of any cross-sectional shape.

PLUMB BOB – Weight hung on the end of a cord so that when the latter is supported at its top end the cord will hang vertical.

PNEUMATIC MICROMETER – An instrument designed to measure, among other things, the errors in the size, shape and alignment of bores, with compressed air.

PROTRACTOR – Instrument graduated so as to enable the measurement of angles to be made in degrees.

PYROMETER – Specified type of thermometer used to measure high temperatures in the production and heat treatment of metals and alloys.

RADIUS GAUGE – Tool used for checking the radius of small fillets or rounded corners.

RECORDING INSTRUMENTS – Instruments which provide a permanent record of readings such as steam pressure, steam flow, air flow, flue gas temperature, feed water temperature, fuel flow and fuel temperature.

RING GAUGE – A gauge in which the inside measuring surfaces are circular in form. A ring gauge may be cylindrical or conical, plain or threaded.

SCLEROSCOPE – Instrument for measuring hardness.

SCREW GAUGE – Type of gauge for checking the accuracy of a screw thread.

SCREW PITCH GAUGE – A small tool with a number of blades, each having the same number of notches per inch as the thread it represents. It is used to find the pitch and number of threads per inch on a screw, tap or die.

SCREW THREAD MICROMETER – Type of micrometer with measuring points specially shaped to enable the measurement of pitch diameter and thickness of thread.

SCRIBER – Used for making lines on the work when marking off.

SINE BAR – Tool used for the accurate setting out of angles by arranging to convert angular measurements to linear ones.

SLIP GAUGE – Form of gauge made of hardened steel with two parallel faces worked to high precision and at a known distance apart.

SNAP GAUGE – A type of fixed gauge, plain or adjustable, arranged with inside measuring surfaces for checking diameters, lengths, thicknesses or widths of work-pieces.

SPRING CALIPERS – Inside or outside calipers for measuring work-pieces in which the tension against the nut is maintained by a circular spring at the end.

STEEL RULE – A thin flat measuring tool graduated in either fractional or decimal part of an inch or cm and made in many styles and lengths.

STRAIGHT EDGE – Strip of metal, usually steel, with one edge straight, used to determine the flatness of a surface.

SURFACE GAUGE – Tool used for marking out and setting up work in conjunction with a surface plate, used also for levelling work-pieces when fixing them to the worktables of machine tools e.g., planers, shapers, millers etc.

TAPER PLUG GAUGE – A solid internal gauge in the form of a frustum of a cone having diameter, taper and length suitable for measuring the dimensions of an internal taper of specified size.

TAPER RING GAUGE – An external gauge, the internal diameter of which confirms to the frustum of a cone having diameter, taper and length suitable for measuring the dimensions of an external taper of specified size.

TEMPLATE – A flat pattern or guide plate usually made from sheet metal and used as a gauge or guide when laying out, drilling, forming in a machine or filing irregular shapes on metal work-pieces.

TELESCOPING GAUGES – Adjustable gauges which consists of a handle attached to a fixed contact within which a plunger contact expands or telescopes under spring tension when the gauge is inserted into the hole that is to be measured.

THREAD GAUGE – Tool for checking the form and pitch of screw threads.

TOOL MAKERS MICROSCOPE – Instrument used in accurate inspection of thread forms, form tools and complex contours.

TORQUE METER – Torsion measuring device fitted to a rotating shaft or component to measure the torque developed at any given moment under actual running conditions.

TORSIOGRAPH – Instrument used to measure and record the amplitude and frequency of torsional vibrations in a rotating shaft or other part.

TRAMMELS – are generally used for laying off and checking dimensions of several feet, they are generally used in conjunction with a large steel rule, which may be from 3 to 10 ft long.

TRANSFER CALIPER – A caliper designed to take measurement in recesses or over a projection. One leg can be separated or opened to remove the caliper and then returned to the measured size.

TRY SQUARE – Instrument used for setting and checking a line, an edge or a face which is required to be at right angles to some other plane which should be regarded as a datum or reference plane.

VACUUM GAUGE – Gauge used to measure the amount of vacuum in any vessel in which a pressure lower than atmospheric pressure is produced by evacuation of air, vapour and gas.

VERNIER – Small-scale, for making accurate measurement, carrying a certain number of graduations equalling in their combined length a different number of graduations, usually one more or one less, on the main scale of the instrument to which the Vernier is attached.

VERNIER CALIPER – Precision measuring instrument consisting of a beam or rule having a fixed jaw at one end, and a straight jaw to which is attached a Vernier scale.

WATER GAUGE – A gauge that shows the proper water level which must be maintained in a boiler to avoid overheating damage.

WIRE GAUGE – Sizes of standard wire and sheet metal are normally expressed not by a dimension in cm, but by a number or gauge size.

WHITWORTH GAUGE – Type of plug, and caliper gauge introduced by Joseph Whitworth.

WICKMAN GAUGE – Special form of adjustable snap or horse shoe type of gap gauge.