ACCURATE – Without error within tolerances allowed, precise, correct, confirming exactly to standard.
ACME THREAD – A screw thread having an included angle of 29° and largely used for feed screws on machine tools.
ACUTE ANGLE – An angle which is less than a right angle, 90°.
ADDENDUM – The portion of the tooth of a gear that extends from the pitch line to the outside.
ALIGN – To bring two or more components of a unit into correct positions with respect to one another.
ALLOWANCE – The intentional or desired difference between the maximum limits of mating parts to provide a certain class of fit.
ANGLE – The amount of opening or divergence between two straight lines that meet at a vertex or that intersect each other.
ANGLE OF THREAD – The included angle between the sides forming the groove of the screw thread.
ANNULUS – A figure bounded by concentric circles or cylinders (e.g.,a washer, ring, sleeve etc.).
ARC – A circular section of the circumference of a circle bounded by two equal radii.
ASSEMBLY – A unit that contains the parts that make up a mechanism or a machine.
AXIS – The line real or imaginary, which passes through the center of a body and about which the body would rotate if set revolving.
BACKLASH - The clearance or amount of movement between the tooth profiles of a pair or train of gears in mesh. Also refers to the looseness or lost motion between screw threads which have been badly worn.
BAFFLE - A device which slows down or diverts the flow of gases, liquid, sound etc.
BASIC SIZE - The theoretical or nominal standard size from which all variations are made.
BASTARD - Not standard, irregular. A bastard cut file is a rough cut file having coarse teeth than a second cut file.
BELL MOUTHED HOLE - A hole which is rounded or tapered slightly larger at one end or both ends and is not exactly cylindrical throughout its entire length.
BEVEL - Any surface not at right angle to the rest of the workpiece. If a bevel is at a 45° angle, it is frequently called a MITER.
BIMETALLIC STRIP - A strip of metal consisting of one metal (or alloy) in the top portion bonded to a different metal in the bottom portion.A straight strip becomes curved when heated.
BLIND HOLE - A hole which is made to a certain depth of a workpiece but does not pass through it.
BISECTING AN ANGLE - Dividing an angle into two equal parts.
BOND - The holding together of different parts.
BORE - The inside diameter of a cylinder, or a hole for a shaft. Also the operation of machining a circular hole in a metal workpiece.
BRUSH - Pieces of carbon or copper that make a sliding contact against the commutator or slip rings.
CAM - A plate or cylinder which transmits variable motion to a part of a machine by means of a follower.
CAP SCREW - A finished screw 5mm or larger, used for fastening two pieces together by passing the screw through a clearance hole in one part and screwing in into a tapped hole in the other.
CENTER - A fixed point about which the radius of a circle or an arc moves.
CENTER LINE - A line used on drawings to show the centers of objects and holes. The center line consists of alternate long and short dashes.
CHAMFER – To bevel or remove the sharp edge of a machined part.
CHECK VALVE – A valve which permits flow in one direction only.
CIRCULAR PITCH – The distance from the center of one gear tooth to the center of the next gear tooth measured on the pitch line.
CIRCUMFERENCE – A curved line forming a circle and the length of this line.
COIL SPRING – A spring steel wire wound in a spiral pattern.
COMMUTATOR – A number of copper bars connected to the armature windings but insulated from each other and from the armature.
CONVOLUTION – One full turn of screw.
CORE – The central or innermost part of an object.
COUNTER BORING – The operation of enlarging a portion of a hole for part of its depth and to a given diameter, as for the head of a fillister head screw.
COUNTER SINK – To cut or shape a depression in an object so that the head of a screw may set flush or below the surface.
CREST CLEARANCE – Defined on a screw form as the space between the top of a thread and the root of its mating thread.
CREST OF SCREW THREAD – The top surface joining the two sides of flanks of a thread.
CROWNED – A slight curve in a surface e.g., on a roller or race way.
DEDENDUM – The depth of a gear tooth space below the pitch line or circle. Also, the radial distance between the pitch circle and the root circle, which also includes the clearance.
DIAPHRAGM – A flexible dividing partition separating two compartments.
DOUBLE FLARE – A flared end of the tubing having two wall thickness.
DOWEL – A pin, usually of circular shape like a cylinder, used to pin or fasten something in position temporarily or permanently.
DRIFT PIN – A round tapered steel pin used to align rivet holes so that the rivet will pass through the holes easily.
ECCENTRIC – A circle or cylinder having a different center from another coinciding circle or cylinder. Also, a device for converting rotary motion to reciprocating motion.
END PLAY – As applied to a shaft, the amount that the shaft can move backward and forward.
EYE BOLT – A bolt threaded at one end and bent to a loop at the other end.
FEATHER – A sliding key, sometimes called splint. Used to prevent a pulley, gear or other part from turning on a shaft but allows it to move lengthwise. The feather is usually fastened to the sliding piece.
FILLET – A concave surface connecting the two surfaces meeting at an angle.
FLANGE– A metal part which is spread out like a rim, the action of working a piece or part to spread out.
FLANK (Side of thread) – The straight part of the thread which connects the crest with the root.
FLARE – To open or spread outwardly.
FULCRUM – The pivot point of a lever.
FLUSH – When the surfaces of different parts are on the same level, they are said to be flush.
FLUTE – A straight or helical groove of angular or radial form machined in a cutting tool to provide cutting edges and to permit chips to escape and the cutting fluid to reach the cutting edges.
GATE VALVE – A common type of manually operated valve in which a sliding gate is used to obstruct the flow of fluid.
GEAR – A general term applied to types of toothed wheels, valve motion, pump works, lifting tackle and ropes.
GEARING – A train of gears or an arrangement of gears for transmitting motion in a machinery.
GIB – An angular or wedge like strip of metal placed between two machine parts, usually sliding bearings, to ensure a proper fit and provide adjustment for wear.
GLAND – A device to prevent the leakage of gas or liquid past a joint.
HAND WHEEL – Any of the various wheels found on machine tools for moving or positioning parts of the machine by hand feed, as the tail stock hand wheel on a lathe.
HALF MOON KEY – A fastening device in a shape somewhat similar to a semicircle.
HELICAL GEAR – A gear in which the teeth are cut at some angle other than a right angle across the gear face.
HELICOIL – A thread insert used to repair worn or damaged threads. It is installed in a retapped hole to bring the screw thread down to original size.
HELIX – The curve formed by a line drawn or wrapped around a cylinder which advances uniformly along the axis for each revolution, as the thread on a screw or the flute on a twist drill. A helix is often called a
spiral in the shop.
HELIX ANGLE OF A THREAD – The angle made by the helix of the thread at the pitch diameter line with a line at right angle to the axis.
HEXAGONAL NUT – A nut having six sides and shaped like a hexagon.
INVOLUTE GEAR TOOTH – A curved tooth generated by unwinding a string from a cylinder to form the curve.
JOURNAL – The part of a shaft or axle that has been machined or finished to fit into a bearing.
KEYS – Metal pieces of various designs that fit into a slot in a shaft and project above the shaft to fit into a mating slot in the center hole of a gear or pulley to provide a positive drive between the shaft and the gear
or pulley.
KEY-SEAT– The slot or recessed groove either in the shaft or gear, which is made to receive the key. Also, it is called a KEYWAY.
KNURL – A uniform roughened or checked surface of either a diamond, a straight or other pattern.
LAND – The top surface of a tooth of cutting tools, such as taps, reamers and milling cutters.
LEAD ANGLE – The angle of the helix of a screw thread or worm thread. It is the measure of the inclination of a screw thread from a plane perpendicular to the axis of the screw.
LEAD HOLE – A small hole drilled in a workpiece to reduce the feed pressure, aid in obtaining greater accuracy, and guide a large drill. Sometimes called PILOT HOLE.
LEAD OF THREAD – On a single threaded screw, the distance the screw or nut advances in one complete revolution.
LEFT HAND SCREW – One that screws into the mating part or advances when turned to the left or counter clockwise.
LIMITS OF SIZE – The minimum and maximum sizes permissible for specific dimensions.
LINE – A tube, pipe or hose which is used as a conductor of fluid.
LINKAGE – A movable connection between two units.
LOBE – The projecting part such as rotor lobe or the cam lobe.
LOCK NUT – A type of nut that is prevented from loosening under vibration. The locking action is accomplished by squeezing, gripping or jamming
against the bolt threads.
LOOSE PULLEY – A pulley which turns freely on a shaft so that a belt can be shifted from the driving pulley to the loose pulley in order to stop a machine driven by an overhead belt drive.
MAJOR DIAMETER – On a straight thread, the diameter of the imaginary cylinder that just touches the crest of an external thread or the root of an internal thread.
MALE PART – The external part of any workpiece which fits into a hole, slot or groove of the mating part.
MANUAL VALVE – A valve which is opened or closed or adjusted by hand.
MESH – Engaging one part with another, as the teeth of one gear mesh with the teeth of a mating gear.
MICRON – One millionth of a meter or 0.039370 inch.
MINOR DIAMETER – On a straight thread, the diameter of the imaginary cylinder which just touches the root of an external thread or the crest of an internal thread.
MORSE TAPER – A self holding, standard taper largely used on drilling tools, drilling machine spindles, and some lathes.
MULTIPLE THREADED SCREW – A screw with two or more threads cut around the periphery of the workpiece to provide an increased lead with a specified pitch.
NUT – A metal fastener of square, hexagon or other shape, having an internal thread which screws onto a bolt, stud or arbor.
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