Maharashtra SSC Engineering Drawing ITI key terms

A flat rectangular wooden or plastic surface with a straight working edge, used to hold drawing paper steady while instruments slide along its edge. Its edges must be truly straight and square to each other.

A drafting tool with a long straight blade fixed at right angles to a short stock. The stock rests against the drawing board edge, so the blade gives a reliable horizontal reference line for parallel work.

A triangular instrument with angles of 45-45-90 or 30-60-90 degrees. Used with a T-square or straight edge to draw lines at 30, 45, 60 and 90 degrees and their combinations.

A semicircular or circular graduated scale marked in degrees, used to measure and set off angles that cannot be obtained with set squares alone.

A V-shaped instrument with two legs joined by a hinge, one holding a needle point and the other a lead or pen, used to draw circles and arcs of a set radius.

A hinged instrument with two sharp steel points, used to transfer measurements from a scale to the drawing and to divide lines or arcs into equal parts.

A thin template with a varying curved edge, used to draw smooth irregular curves through a series of plotted points that a compass cannot handle.

Standard trimmed paper dimensions designated A0, A1, A2, A3 and A4, each obtained by halving the previous size. A0 is one square metre, and the series keeps a constant width-to-length ratio.

A ruled panel, usually at the bottom right of the sheet, recording part name, drawing number, scale, material, date, and the names of the draughtsman and checker.

The fixed ratio between a length on the drawing and the corresponding real length of the object, stated as reducing, full size, or enlarging.

The ratio written as a fraction, such as 1:20, expressing drawing length over actual length. It identifies at a glance whether a drawing is reduced or enlarged.

The standard families of line used on a drawing, including continuous thick for visible outlines, continuous thin for dimensions and hatching, dashed for hidden edges, and chain for centre lines.

A short-dashed thin line showing an edge or contour that is not visible from the viewing direction but is needed to describe the object completely.

A long-and-short chain line drawn through the axis of a symmetrical feature such as a hole, cylinder or bolt circle, marking its centre and axis of symmetry.

Standard single-stroke capital writing used for notes, dimensions and titles. It must be legible, uniform in height and slope, and follow the prescribed stroke order and proportions.

A thin continuous line terminated by arrowheads that shows the extent of a dimension, with the value written above it or in a gap in the line.

A thin line drawn from the feature being measured, at right angles to the dimension line, showing where the dimension starts and ends. It stops short of the object outline.

A thin line with an arrowhead at one end, pointing to a feature and carrying a note, symbol or dimension value that cannot be placed beside the feature itself.

The step-by-step drawing of shapes such as bisected angles, perpendiculars, polygons and tangent arcs using only compass, straight edge and set squares, without measurement of angles.

A closed plane figure with all sides equal and all interior angles equal, such as a pentagon or hexagon, usually constructed inside or outside a given circle.

A closed curve traced by a point whose distances from two fixed foci always add to a constant sum. Constructed by concentric circles, oblong or trammel methods.

A straight line or curve that touches another curve at exactly one point without crossing it. Tangent constructions join arcs smoothly to lines and to each other.

A method of representing a three-dimensional object by separate two-dimensional views projected onto planes at right angles, with the observer assumed at infinity so projectors are parallel.

A projection system in which the object lies between the observer and the plane, so the view seen from the front is placed below the front view on the sheet.

A projection system in which the plane lies between the observer and the object, so the top view appears above the front view and the right-side view appears on the right.

The three mutually perpendicular reference planes, horizontal, vertical and profile, onto which top, front and side views of an object are projected.

The actual undiminished length of a line, seen when the line is parallel to a plane of projection. Found by rotation or auxiliary-plane methods when the line is inclined.

The angle a line or plane makes with a principal plane of projection, denoted by theta with the horizontal plane and phi with the vertical plane.

A view projected onto an extra plane inclined to a principal plane, used to show the true shape of an inclined face or the true length of an inclined line.

Drawing the front and top views of three-dimensional bodies such as prisms, pyramids, cylinders and cones in simple, inclined or resting-on-a-face positions.

The straight centre line about which a solid such as a cylinder, cone or prism is generated or about which it is symmetrical. Its position fixes the solid's orientation.

The portion of a solid left when its top is cut off by a plane parallel to the base, as in a frustum of a cone or pyramid.

An imaginary cutting plane passed through an object to reveal internal detail. Its position is shown by a chain line with thick ends and arrows giving the viewing direction.

A view showing the cut surface and the visible edges behind it after the object has been imagined cut by a section plane and the nearer part removed.

Thin equally spaced parallel lines at 45 degrees drawn across a cut surface to distinguish solid material from empty space in a sectional view.

The true-shape flat pattern of a hollow solid's surface, laid out so it can be cut from sheet metal and folded back into the original shape.

A method of developing surfaces of prisms and cylinders by dividing the surface into parallel elements, projecting their true lengths, and laying them out side by side.

A method of developing surfaces of pyramids and cones by treating the surface as triangles or sectors radiating from an apex, using true lengths of slant edges.

A pictorial projection in which the three axes are equally inclined at 120 degrees to each other and all are foreshortened equally, giving a single view that shows three faces.

A scale of 0.816 times true length used to set off dimensions along isometric axes so the drawing matches a true isometric projection rather than an isometric view.

A pictorial projection in which the front face is drawn true shape and size, while receding edges are drawn at an angle, usually 45 degrees, often at half scale.

The total permissible variation in a dimension, equal to the difference between the upper and lower limits. It defines how much a part may deviate and still function.

The two extreme permitted sizes of a feature, the maximum and minimum limits, between which the actual measured size must fall for the part to be accepted.

The relationship between the tolerance zones of a hole and a shaft assembled together, classified as clearance, interference or transition depending on whether play or tightness results.

A device such as a bolt, nut, screw, rivet or key used to hold two or more parts together, either permanently or so they can be dismantled.

The standard simplified representation of screw threads, using thin and thick lines for crests and roots, with hidden lines omitted and thread depth shown by convention rather than true profile.

A small piece of metal inserted in matching keyways in a shaft and hub to prevent relative rotation while allowing the parts to be assembled and dismantled.

The longitudinal slot cut in a shaft and in the mating hub to seat a key. Its depth and width are dimensioned to suit the key cross-section.

A device joining the ends of two shafts to transmit rotation, either rigidly, as with a flanged coupling, or flexibly to absorb misalignment.

A machine element that supports a rotating shaft, reduces friction and carries radial or axial load, shown in assembly drawings by its housing, bush or rolling elements.

Drawing without instruments, using light construction lines and correct proportions to record an object quickly, often as a preliminary to a formal instrument drawing.

The skill of interpreting views, symbols, dimensions and notes on a drawing so as to visualise the shape of the part and understand how it is to be made.