Lines, Lettering and Dimensioning
This domain tests whether you can select the correct line, letter a drawing legibly, and dimension it without ambiguity.
Lines (IS 10714)
Visible outlines: continuous thick. Hidden edges: short dashes, evenly spaced. Centre lines and pitch circles: long-dash short-dash chain thin. Cutting planes: chain thick at ends and changes of direction. Dimension, extension, leader and hatching lines: continuous thin. Break lines: continuous thin freehand or ruled with zigzag. Construction lines: thin and light, not part of the finished drawing.
Lettering (IS 9609)
Use upright or 75° inclined capital letters. Heights from the preferred series 2.5, 3.5, 5, 7, 10, 14, 20 mm. Stroke width is about h/14 for type A and h/10 for type B. Keep letters of one word the same height; spacing between letters about 2 mm for 5 mm lettering.
Dimensioning (IS 11669)
Dimension lines are thin, with closed filled arrowheads about 3 mm long. Extension lines start 1 mm from the object and extend 2–3 mm past the dimension line. Numerals sit above the dimension line in the aligned system, or horizontally in the unidirectional system. Use Ø for diameter, R for radius, SØ for a spherical diameter, □ for a square, and t for thickness.
Worked example
A plate has a 40 mm diameter hole. Write Ø40, not R40 or 40Ø. The leader touches the circle and points to the centre; the arrowhead is outside if space is tight. If the hole is 20 mm radius, write R20. A 40 mm square is □40.
Traps
Dimensioning a hidden line; repeating the same size in two views; using a centre line as an extension line; putting the arrowhead backwards; mixing aligned and unidirectional numerals; giving the radius as a diameter.