Part 1 of 2
Drawing Instruments, Standards, Lines & Lettering
Last reviewed 16 Sept 2026 · 7 min read
Engineering drawing
Engineering drawing is the graphic language of engineers — a precise, standardised way of communicating the shape, size, material and construction details of objects and structures. Unlike artistic drawing, it follows standards so that it is interpreted uniformly.
In India, engineering drawing practice is standardised by the Bureau of Indian Standards in SP 46 (Engineering Drawing Practice for Schools and Colleges), which is based on ISO standards. IS 962 deals with architectural and building drawings.
Drawing instruments and materials
| Instrument / material | Use |
|---|---|
| Drawing board | Flat wooden board with a straight working edge; sizes such as D0, D1, D2 to suit sheet sizes |
| Mini-drafter | Clamped to the board; two perpendicular scales with a protractor head — draws horizontal, vertical and inclined lines quickly (replaces T-square, set squares and protractor) |
| T-square | Horizontal parallel lines (used against the board edge) |
| Set squares | 45° and 30°–60° triangles — vertical and inclined lines; combined to draw lines at 15° intervals |
| Protractor | Measuring and setting angles |
| Scales | Plastic/boxwood scales with different reduction ratios; engineer's scale set |
| Large compass | Circles and arcs (with lengthening bar for large radii) |
| Bow compass | Small circles and arcs |
| Dividers | Transferring distances and dividing lines into equal parts |
| French curves | Drawing irregular (non-circular) curves smoothly through plotted points |
| Templates / stencils | Circles, ellipses, symbols, lettering |
| Pencils | Grades from 9H (hardest) to 9B (softest); H = hard, B = black/soft, HB = medium. Typically 2H/H for construction lines, H/HB for finished lines, HB for lettering |
| Clutch/mechanical pencils | Constant line width (0.3, 0.5, 0.7 mm leads) |
| Erasers and erasing shield | Clean removal of selected lines |
| Drawing clips / adhesive tape | Fixing the sheet |
| Sandpaper block | Sharpening pencil leads (conical or chisel point) |
Drawing sheets
Sizes (ISO A-series, trimmed sizes)
| Designation | Size (mm) |
|---|---|
| A0 | 841 × 1189 |
| A1 | 594 × 841 |
| A2 | 420 × 594 |
| A3 | 297 × 420 |
| A4 | 210 × 297 |
- A0 has an area of 1 m²; each smaller size is obtained by halving the longer side of the previous size.
- Sides are in the ratio 1 : √2, which is preserved on halving.
Layout of a drawing sheet
- Borders — a wider margin (commonly about 20 mm) on the left edge for filing/binding, and narrower margins (commonly about 10 mm) on other sides.
- Title block — at the bottom right-hand corner, containing name of institution/organisation, title of drawing, drawing number, scale, projection symbol, date, names/signatures (drawn, checked, approved), sheet number and revisions.
- Revision table, parts list (for assemblies) above the title block.
- Folding marks and grid reference system on large sheets.
- Orientation — sheets used in landscape or portrait as convenient; title block always readable in the normal viewing direction.
Lines
Types of lines (SP 46 / ISO)
| Line | Description | Applications |
|---|---|---|
| A | Continuous thick | Visible outlines and edges |
| B | Continuous thin (straight) | Dimension lines, extension (projection) lines, leader lines, hatching (section lines), short centre lines, imaginary lines of intersection |
| C | Continuous thin freehand | Short break lines, limits of partial views |
| D | Continuous thin with zigzags | Long break lines |
| E / F | Dashed (thick / thin) | Hidden outlines and edges |
| G | Chain thin (long dash–dot) | Centre lines, lines of symmetry, trajectories, pitch circles |
| H | Chain thin, thick at ends and at changes of direction | Cutting planes (section planes) |
| J | Chain thick | Surfaces with special requirements (e.g. heat treatment) |
| K | Chain thin double-dashed | Outlines of adjacent parts, alternative/extreme positions of moving parts, centroidal lines |
Line thickness and precedence
- Two thicknesses are used, with thick lines about twice the thickness of thin lines (e.g. 0.5 mm and 0.25 mm, or 0.7 mm and 0.35 mm).
- Order of precedence when lines coincide: visible outline > hidden line > cutting plane line > centre line > projection/dimension lines.
- Dashes of hidden lines and chain lines should be uniform; centre lines should extend slightly beyond the outline and cross at long dashes, not at gaps.
- A hidden line meeting a visible line should start with a dash touching it (or a gap where it continues the visible line).