Engineering Drawing Symbols: Complete Reference Guide

Engineering drawing symbols communicate the entire intent of a design in a fraction of the space a written specification would take. A single fillet-weld symbol with a tail call-out replaces a paragraph of weld description. A surface-finish check-mark with a 1.6 underneath replaces three sentences about machining. A counterbore symbol followed by a diameter and depth replaces a manufacturing instruction. The catch: every symbol depends on the reader knowing the convention. Misread a third-angle projection as first angle and the part comes back mirrored. Misread an AWS welding symbol as ISO and the weld lands on the wrong side of the joint. The cost of misinterpretation is rework, scrap and warranty claims.

This guide is the comprehensive reference for engineering drawing symbols used on Australian industrial drawings — line types, view conventions, dimensioning, hole features, threading, surface finish, welding, hydraulic and pneumatic schematics, and the broader categories that define a complete engineering drawing. AS 1100 (the Australian Standard for technical drawing) sets the rules; ISO and ASME standards govern parallel international content. Where the two diverge, the differences are flagged — particularly around projection systems and welding-symbol conventions, where misreading is the most common and most costly error.

For the dedicated deep-dive on geometric dimensioning and tolerancing — the 14 GD&T symbols, datum reference frames, feature control frame parsing, and MMC/LMC modifiers — see our companion GD&T Symbols Reference Guide. This article covers the broader landscape that surrounds GD&T on every drawing: the lines, views, dimensions, finishes, welds and schematics that the GD&T symbols sit alongside.

Australian Standard AS 1100 — the rules behind every drawing

AS 1100 is the Australian Standard for technical drawing. It is a multi-part standard published by Standards Australia / Standards New Zealand under committee ME-072. The series defines line types, view projection conventions, dimensioning rules, surface finish notation, welding-symbol conventions, sectioning practices and drawing-sheet layout requirements that apply to drawings produced for Australian industry.

The structure of the AS 1100 series matters because different parts apply to different drawing types — a mechanical engineering drawing follows AS 1100.201, an architectural drawing follows AS 1100.301, and the general principles applying to all of them sit in AS 1100.101.

Two practical points apply to anyone reading or drawing on AU drawings:

1. AS 1100 specifies third-angle projection. The view above the front view is the top view (projected as if folded down onto the same plane). This matches the United States convention, but is opposite to first-angle projection used in Europe and most of the rest of the world. Drawings imported from European OEMs (Bosch, Festo, Siemens, SKF, Schaeffler) typically use first-angle projection — read carefully or the views interpret backwards.
2. AS 1100 references ISO standards for component-level symbols. Welding symbols follow ISO 2553 (with AWS A2.4 as the alternative used by many drawings of US origin). Surface finish symbols follow ISO 1302. Geometric tolerancing follows ISO 1101 and ASME Y14.5. Hydraulic and pneumatic schematic symbols follow ISO 1219-1.

Line types — the alphabet of drawing

Every line on an engineering drawing means something. Line type and line weight together encode the message — visible edges in thick continuous lines, hidden edges in thin dashed lines, centrelines in thin chain lines, and so on. AS 1100.101 defines ten standard line types. Most drawings use eight of them routinely; the other two appear in specific contexts (cutting plane and chain).

The two-line-weight convention is fundamental: thick lines for visible edges and cutting planes, thin lines for everything else. Drawings without weight differentiation become very hard to read at scale.

Dashed (hidden) lines should always start and end with a dash where they meet a visible line — gaps at the join point indicate a different feature. Centrelines start and end with the long stroke (not the short dash), and a small cross at the centre of a circle marks the centre of a hole or shaft.

View conventions — first angle vs third angle, orthographic, isometric, section

The view convention is set by a small symbol in the title block — a truncated cone with two views projected next to it. If the cone shape sits to the LEFT in the side view, the drawing is third angle (AS 1100, US convention). If it sits to the RIGHT, the drawing is first angle (European and most international convention). Confirm this before reading any drawing. Reading a first-angle drawing as third-angle puts every view on the wrong side of the page.

Standard view types appear on most engineering drawings:

The most common reading mistake — the projection trap. A drawing produced in Germany, France or Italy is almost certainly first-angle projection. A drawing produced in Australia, New Zealand or the United States is almost certainly third angle. If your part comes back mirrored, the projection convention was misread. Check the truncated-cone symbol in the title block before doing anything else.

Dimensioning conventions

Dimensions on an engineering drawing communicate size, location, and tolerance. AS 1100 prescribes how dimensions are placed, what symbols precede them, and how they are toleranced. The principles below cover the symbols and conventions that appear on most drawings — the dimensioning rules themselves (chain vs parallel vs ordinate, where to place dimensions, when to use bilateral vs unilateral tolerances) are large topics in their own right.

Default unit on AU mechanical drawings is millimetres — units may not be stated unless an exception applies (a metric drawing dimensioning a single feature in inches, for example, would label that dimension explicitly). Default angle unit is degrees (decimal — not degrees-minutes-seconds, except on survey drawings under AS 1100.401).

Where dimensions are not toleranced individually, the title block specifies a default tolerance — typically 1-decimal-place dimensions ±0.1 mm, 2-decimal-place ±0.05 mm, no-decimal ±0.5 mm. Always read the title block default tolerance before assuming anything about a feature.

Hole feature symbols — counterbore, countersink, depth, spotface

Hole feature symbols are the second-most-cited symbols on a typical mechanical drawing (after dimensions themselves). Each symbol replaces a multi-word feature description and combines with the diameter and depth values to fully specify the hole. The tools that produce these features — drill bits, step drills, counterbores and countersinks — sit in our drilling tool range.

Reading order matters. The symbol always precedes the dimension. Ø6.6 ⌴ Ø11 ↧6 reads as: drill 6.6 mm hole all the way through, then counterbore an 11 mm diameter recess 6 mm deep on the entry side. The depth value applies to the immediately preceding feature (the counterbore), not the through hole.

For deep coverage of counterbore size selection (matching counterbore dimensions to socket-head-cap-screw heads, the M3–M24 reference table, and the choice between counterbore and countersink for different fastener types), see our Counterbore Drill Bits and Countersink Reference.

Threading symbols and callouts

Thread callouts encode the thread system, nominal size, pitch, tolerance class, length and direction. AU industrial drawings use four common systems: metric ISO (M), British Standard Pipe (BSP, both parallel G and tapered Rp/Rc), Unified National Coarse and Fine (UNC/UNF), and National Pipe Taper (NPT). Each system has its own callout convention. AIMS stocks the complete threading range — taps, dies, threading inserts and gauges across all four systems.

Threads on engineering drawings are typically shown using simplified or schematic representation — a circle pattern with crests and roots indicated by thin lines, rather than the helical reality. ISO 6410 and AS 1100.201 specify these conventions. Do not attempt to model true helical threads on production drawings — it adds visual noise without adding manufacturing information.

For full coverage of pipe-thread standards, BSP vs NPT incompatibility and the AS 1722 series, see our Hydraulic Fittings and Pipe Thread Standards Guide. For metric vs imperial fastener thread conventions in Australian industry, see our Metric vs Imperial Fasteners.

Surface finish symbols

Surface finish (also called surface roughness or surface texture) describes how smooth or rough a machined surface is, measured in micrometres of roughness (Ra, the most common measure, is the arithmetic mean deviation from the mean line over the sampling length). The symbol is a check-mark with the apex resting on the surface to be specified, with optional additions for the finish requirement, value, lay direction and machining method. Verifying surface finish and dimensional accuracy to drawing tolerance generally needs precision instruments — see our micrometers and dial indicators ranges.

Common Ra values on Australian industrial drawings:

Lay direction — the direction of the surface texture pattern — is indicated by a symbol added to the lower-left of the basic check-mark:

Old vs new surface finish notation — the legacy drawing trap. Drawings produced before ISO 1302:2002 used a different set of symbols: 1, 2, 3, or 4 triangles (V, VV, VVV, VVVV) or N-grades (N1 through N12) to indicate finish quality. Older AU industrial drawings — particularly maintenance drawings and equipment manuals — still circulate with these. One triangle (V) ≈ 25 µm Ra. Two triangles (VV) ≈ 6.3 µm. Three triangles (VVV) ≈ 1.6 µm. Four triangles (VVVV) ≈ 0.4 µm. N-grade conversion: N1 = 0.025 µm Ra (super finishing), N4 = 0.2 µm (grinding), N7 = 1.6 µm (fine turning), N9 = 6.3 µm (medium turning), N12 = 50 µm (rough machining). If the drawing predates 2002, expect old notation.

A surface finish symbol with no value typically refers to the title block default ("all surfaces machined to N7 unless otherwise specified" is a common note). Where Rz, Rt, Rmax or other parameters are specified instead of Ra, the parameter is shown alongside the value: "Rz 6.3" rather than "1.6" with the assumption of Ra.

Welding symbols — AWS A2.4 vs ISO 2553

Welding symbols pack an enormous amount of information into a small footprint: weld type, size, length, location relative to the joint, finish, contour and process — all within a single arrow-and-reference-line construct. The catch: AWS A2.4 (American convention, used by ASME-coded welds) and ISO 2553 (the international convention referenced by AS 1100) place the weld symbol on opposite sides of the reference line. Reading mixed-source drawings without checking the convention puts welds on the wrong side of the joint. The consumables and equipment needed to execute these weld callouts in steel, stainless and aluminium sit in our welding range.

The basic weld type symbols replace verbal descriptions:

Numeric values around the symbol carry specific meanings: the leg size to the LEFT of the symbol, length and pitch to the RIGHT (e.g. "6 fillet, 50 long, 100 centre-to-centre" = 6 mm fillet weld 50 mm long every 100 mm), depth of penetration in parentheses BEFORE the symbol, and process code or reference in the tail.

The most common welding-symbol error — wrong side of joint. AWS and ISO place weld symbols differently. AWS: symbol BELOW the reference line means the arrow side, symbol ABOVE means the other side. ISO 2553 keeps the same arrow/other side convention but adds a DASHED reference line above the solid one for the other-side weld — making it explicit. Mixed-source drawings (AU drawings referencing US-OEM components) need the convention checked at the title block before any weld is laid. The cost of getting it wrong is rework on a structural weldment.

Hydraulic and pneumatic schematic symbols (ISO 1219-1)

Hydraulic and pneumatic systems are documented using schematic symbols rather than physical layouts. ISO 1219-1 ("Fluid power systems and components — Graphical symbols and circuit diagrams") defines the standard set used worldwide. The symbols are abstract — a circle is a pump or motor, a square is a valve, a rectangle is a cylinder — but each combines with internal arrows and ports to specify exact function.

For pneumatic systems the same ISO 1219-1 symbols apply, with two additions: an open arrow at a vented connection (atmospheric exhaust) and a circle-with-line for compressed-air sources. Hydraulic symbols are typically drawn with solid triangles indicating fluid power flow; pneumatic symbols use open triangles for compressed-air flow.

The schematic is read by following fluid flow from source (pump or compressor) through valves to actuators (cylinders, motors) and back to tank or atmosphere. Each switching position of a directional valve is a separate "box" — the valve in operation is the box currently aligned with the supply lines. Drawing a hydraulic system requires both the schematic (for function) and a separate physical layout drawing (for hose routing, mounting, and physical clearances).

Electrical schematic symbols (overview)

Electrical schematic symbols are governed in Australia by AS/NZS 1102 (graphical symbols for electrotechnical diagrams) and AS/NZS 3000 (the Wiring Rules, which specify the symbols used on installation drawings). Industrial control schematics typically follow IEC 60617 or the older NEMA conventions depending on the equipment origin.

Common families of electrical schematic symbols include: contacts (normally open, normally closed), coils (relay, contactor, solenoid), motor symbols (single-phase, three-phase, DC), protection devices (fuses, circuit breakers, overload relays), sensors (limit switches, pressure switches, temperature switches), and connection symbols (terminals, plugs, sockets). Detailed coverage of electrical schematics sits outside the scope of this article — for installation-drawing symbols and the AS/NZS 3000 framework, refer to the relevant electrical-trade publications.

GD&T symbols — brief overview and deep-dive

Geometric dimensioning and tolerancing (GD&T) is the standardised system for specifying form, orientation, location, profile and runout tolerances on engineering drawings. It uses a defined set of 14 symbols enclosed in feature control frames (FCFs) that reference one or more datums. ASME Y14.5 and ISO 1101 are the primary standards; AS 1100.201 references ISO 1101 for AU drawings.

The 14 GD&T symbols at a glance:

A feature control frame reads left to right: characteristic symbol, tolerance value, material condition modifier (M/L), datum references in order of precedence. Example: a perpendicularity tolerance of 0.05 mm at maximum material condition referenced to datum A reads as perpendicularity 0.05 M A within a single rectangular frame.

For the full deep-dive — every GD&T symbol explained with tolerance zone descriptions, datum reference frame setup, MMC/LMC/RFS modifiers, bonus tolerance and virtual condition with worked examples, common GD&T mistakes, and AS/NZS 1100 / ASME Y14.5 / ISO 1101 standards mapping — see our companion GD&T Symbols Reference Guide. The companion article covers the symbols themselves in depth; this article covers the broader drawing context within which GD&T is interpreted.

Title block, revision triangle, BOM and balloons

Drawing housekeeping symbols are easily overlooked but carry critical information about authority, version control and assembly sequence:

• Title block — bottom-right of the drawing sheet. Contains drawing number, title, scale, sheet size (A0/A1/A2/A3/A4), date, drafted-by, checked-by, approved-by, default tolerances, projection symbol (third-angle truncated cone for AU drawings), units (mm typical), and material/treatment defaults. Always read the title block before starting interpretation.
• Revision block — typically upper-right or above the title block. Lists every change made to the drawing with revision letter (A, B, C…), date, description, and approving authority. A revision triangle (▲ with letter inside) marks each location on the drawing where a change was made.
• Bill of materials (BOM) — listed on the drawing or as a separate sheet for assembly drawings. Each line item has an item number, part number, description, quantity, and material. Item numbers correspond to balloon callouts on the assembly view.
• Balloons — circles with item numbers, connected by leader lines to the parts they represent on the assembly view. Standard practice is to balloon every part listed in the BOM.
• Find numbers / item numbers — small numerals (typically inside a balloon) used to identify individual components on assembly drawings.
• Section view labels — letters (A-A, B-B, C-C) connecting cutting plane lines on the parent view to the corresponding section view drawn separately.
• Detail view labels — circles with letters (X, Y, Z) drawn around features to be magnified, with the corresponding detail view drawn separately at larger scale.

Common confusion points (the forum-mining payoff)

These are the points where engineers, drafters, fitters and machinists report drawing-reading errors most frequently — the ones that cost rework hours.

1. Projection direction misread. First-angle drawings read as third-angle (or vice versa) result in mirrored parts. The truncated-cone symbol in the title block resolves this — if the cone shape sits to the LEFT in the side view, third angle (AS 1100 / US convention). RIGHT, first angle (European convention).
2. AWS vs ISO welding symbol position. AWS: symbol below reference line = arrow side weld. ISO 2553: same convention, but with a dashed reference line above the solid one for other-side welds, making the convention explicit. Drawings of mixed origin require checking the convention.
3. Old vs new surface finish notation. Pre-ISO 1302:2002 drawings use 1/2/3/4 triangles (V/VV/VVV/VVVV) or N-grades (N1–N12). Modern drawings use Ra value with check-mark. Both still appear on AU industrial drawings — the older ones predominantly on legacy maintenance drawings and equipment manuals.
4. Ra vs Rz default assumption. Surface finish is Ra unless explicitly stated. A "1.6" with no parameter prefix means 1.6 µm Ra. Rz, Rt, Rmax and other parameters require explicit notation — and Rz values are typically 4–6× the Ra value of the same surface.
5. Drawings rely on default conventions, not every detail spelled out. Title block default tolerances, default surface finish, default unit (mm), default radius for unspecified internal corners — all apply unless overridden. Reading the title block before interpreting features is essential.
6. Hidden line vs phantom line. Hidden line = continuous short dashes. Phantom line = chain (long-short-short-long). Different meaning: hidden indicates an edge behind a surface, phantom indicates an alternate position, an adjacent part, or repeated detail.
7. Centreline vs cutting plane line. Centreline = thin chain (long-short). Cutting plane line = thick chain (long-short-short) or zigzag. The cutting plane has arrows at each end indicating direction of view; the centreline has no arrows.
8. Counterbore vs spotface. Both use the ⌴ symbol but differ by depth — counterbore is typically 60–100% of fastener-head height (head sits flush or recessed), spotface is shallow (0.5–2 mm) and provides a flat seating surface only. The depth value distinguishes them.
9. BSP vs NPT thread incompatibility. BSP uses 55° thread angle (Whitworth), NPT uses 60° (Sellers). They share TPI values at some sizes (1/2 inch and 3/4 inch both 14 TPI) but cannot mate. The G/Rp/Rc vs NPT callout system signals which is in use — never substitute.
10. Diameter symbol Ø vs DIA abbreviation. The Ø symbol is preferred on modern drawings. "DIA" written out is older AU notation but still appears on legacy drawings. Both mean the same thing.
11. Inch marks (") and foot marks ('). Modern AU drawings should not need these — units default to mm. If they appear, the dimension is imperial and must be converted (or interpreted in the context of an imperial-spec piece of equipment).
12. Reference dimensions in parentheses (85). Reference dimensions are informational only — not to be measured or toleranced. They appear because the dimension is fully constrained by other features but useful to know.

Common mistakes engineers and tradies make reading drawings

1. Skipping the title block. Default tolerances, unit, material, projection convention all live there. Reading geometry without reading the title block is the single most common cause of misinterpretation.
2. Assuming third-angle projection without checking. AU drawings should be third angle but European-OEM drawings imported to AU industrial use are typically first angle. Check the projection symbol every time.
3. Treating reference dimensions as toleranced. Parenthesised dimensions are informational. They are not measured or held to tolerance.
4. Reading welding symbols without checking AWS vs ISO. Always check whether the drawing was produced under AWS A2.4 (US/ASME-coded) or ISO 2553 (international/AU). The dashed reference line is the ISO tell.
5. Misreading Ra default. Surface finish is Ra unless stated. Don't assume Rz from a triangle drawing without checking.
6. Ignoring lay direction symbols. The lay symbol underneath the surface finish check-mark tells the manufacturer which machining direction to use. It matters for sealing surfaces and sliding interfaces.
7. Reading dimension lines without arrowheads as toleranced. Some old drawings use limit dimensions (a number above and a number below) — these define max and min, not nominal and tolerance.
8. Confusing the depth symbol ↧ with the arrow indicator. The depth symbol is a downward arrow with a horizontal bar at the top. It applies to the immediately preceding feature.
9. Misreading partial sections as full sections. Half sections, broken-out sections, removed sections and offset sections each have specific conventions. The cutting plane line indicates which.
10. Assuming all holes are through-holes. A hole without an explicit "THRU" or depth callout may default to through, but check the cross-section. Blind holes need explicit depth.

AIMS position

This is a pure reference asset — one of a handful of EBB-series engineering reference articles AIMS Industrial maintains alongside our product range. We publish reference content like this because the people who specify our products (engineers, designers, draftspeople, maintenance fitters) need fast, accurate reference material at hand. The Engineer's Black Book is the desk-reference for this content in printed form; this article is the online complement.

The Engineer's Black Book covers technical drawing standards, GD&T, surface finish, welding symbols, threading, materials and properties in a single hardcover desk reference designed for daily use.

If you have a question about a specific drawing symbol, an obscure callout, or how an Australian-standard drawing should be marked up, contact the AIMS team — we keep the EBB on every desk and we are happy to answer drawing-symbol questions for customers and the broader engineering community.

Frequently Asked Questions

Quick reference answers to the most common questions on engineering drawing symbols, projection conventions, surface finish notation, welding symbols and AS 1100 standards.

What does the symbol Ø mean on an engineering drawing?

The Ø symbol means diameter. Ø25 means a 25 mm diameter feature — typically a hole or a cylindrical shaft. For radius use R (R5 = 5 mm radius). For spherical diameter use SØ. The symbol always precedes the dimension value. On older Australian drawings the abbreviation 'DIA' written out may appear instead of Ø — both mean the same thing.

What is the difference between first angle and third angle projection?

First angle projection places projected views OPPOSITE the side they would be seen from — the top view goes BELOW the front view, the right-side view goes to the LEFT of the front view. Third angle projection (used in Australia under AS 1100) places projected views on the SAME side they would be seen from — top view ABOVE front, right-side view to the RIGHT. The two systems produce mirror-image layouts. The truncated-cone symbol in the title block indicates which is in use: cone shape pointing left = third angle; cone shape pointing right = first angle.

Which projection convention does Australia use?

Australia uses third-angle projection per AS 1100. This matches the United States convention. First-angle projection is used in Europe, the UK and most of the rest of the world. AU drawings imported from European OEMs (Bosch, Festo, Siemens, SKF, Schaeffler) are typically first-angle and must be read accordingly. Always check the projection symbol in the title block — reading a first-angle drawing as third-angle puts every view on the wrong side of the page.

What does the circle at the apex of a welding symbol mean?

A circle at the junction of the arrow and the reference line means 'weld all around' — the weld is to be made continuously around the joint, not just along the arrow length. This is critical for fully sealed joints, structural connections that need fatigue resistance, and any joint where partial welding would leave a leak path or stress concentration.

Are AWS and ISO welding symbols the same?

Almost — but there is one critical difference. AWS A2.4 (American convention) and ISO 2553 (international convention referenced by AS 1100) use the same basic symbol set: triangle for fillet, V for V-groove, square for square groove, etc. They both use the convention that a symbol below the reference line means the arrow side. The key difference is that ISO 2553 adds a DASHED reference line above the solid one when the weld is on the other side — making the side explicit. AWS does not use the dashed line. Reading mixed-source drawings requires checking the title block to know which convention applies.

What is the symbol for surface finish?

The basic surface finish symbol is a check-mark (similar to a tick) with the apex resting on the surface to be specified. A horizontal bar across the top of the check-mark adds the requirement that material removal is mandatory (machining required). A small circle at the apex adds the requirement that material removal is NOT permitted (the surface stays as-cast, as-forged, or as-rolled). Numeric values inside or beside the symbol specify the maximum surface roughness, typically in micrometres of Ra.

What is a 3.2 surface finish?

A 3.2 surface finish means a maximum surface roughness of 3.2 µm Ra (3.2 micrometres arithmetic mean roughness). This is a typical fine-machined finish achievable by fine turning, fine milling, light drilling or fine reaming — suitable for general mating surfaces, gasket faces, and bearing seats that are not high-precision. Ra 1.6 is one step finer (precision bearing seats, hydraulic cylinder bores), Ra 6.3 is one step rougher (medium turning, general machined surfaces).

What is the difference between Ra and Rz?

Ra is the arithmetic mean roughness — the average deviation of the surface from the mean line over the sampling length. It smooths out individual peaks and valleys. Rz is the average peak-to-valley height of the largest five peaks and valleys in the sampling length — it captures extreme features that Ra averages out. Ra is the default parameter on most modern engineering drawings and is the dominant convention in North America. Rz is more common on European drawings and on surfaces where peak height matters (sealing surfaces, sliding interfaces). Rz values are typically 4–6× the Ra value for the same surface.

What do the old triangle symbols mean on drawings (V, VV, VVV)?

Old surface finish notation used 1, 2, 3, or 4 triangles to indicate finish quality before ISO 1302:2002 introduced the modern system. Approximate equivalents: one triangle (V) ≈ 25 µm Ra (rough turning), two triangles (VV) ≈ 6.3 µm (medium turning), three triangles (VVV) ≈ 1.6 µm (fine turning, light grinding), four triangles (VVVV) ≈ 0.4 µm (fine grinding, honing). Older Australian industrial drawings, particularly maintenance drawings and equipment manuals, still circulate with this notation. The N-grade system (N1 through N12) is a parallel old convention — N7 ≈ 1.6 µm, N9 ≈ 6.3 µm, N12 ≈ 50 µm.

What is the counterbore symbol?

The counterbore symbol is ⌴ (a rectangle with the open side facing down, like an inverted U). It precedes the diameter and depth values: 'Ø6.6 ⌴ Ø11 ↧6' reads as a 6.6 mm hole drilled all the way through, then a counterbore 11 mm in diameter and 6 mm deep on the entry side. The countersink symbol is ⌵ (an inverted V shape) and applies to conical recesses for flat-head screws.

What is the depth symbol on engineering drawings?

The depth symbol is ↧ (a downward arrow with a horizontal bar at the top). It indicates the depth of the immediately preceding feature, measured from the surface. 'Ø8 ↧20' means an 8 mm diameter hole 20 mm deep (a blind hole). The depth symbol applies to the feature it follows — when used after a counterbore symbol it indicates counterbore depth, after a hole diameter it indicates hole depth, and so on.

What does the Australian Standard AS 1100 cover?

AS 1100 is the Australian Standard for technical drawing — a multi-part standard governing how engineering drawings are produced and read in Australia. AS 1100.101 covers general principles (sheet sizes, scales, lettering, line types, projection systems, drawing layout). AS 1100.201 covers mechanical engineering drawings (fasteners, threads, gears, surface finish, welding, GD&T). AS 1100.301 covers architectural drawings. AS 1100.401 covers engineering survey and design drawings. The series is published by Standards Australia / Standards New Zealand. Most AU industrial drawings are produced under AS 1100.201.

What is the difference between a hidden line and a phantom line?

A hidden line uses short dashes (continuous, equal length) and represents an edge that is hidden behind another surface in the current view. A phantom line uses chain pattern (long-short-short-long, repeating) and represents an alternate position of a moving part, an adjacent part shown for context, or repeated detail (such as gear teeth or a series of holes shown only at the ends with phantom lines indicating the pattern continues between). Both use thin line weight, but the dash pattern distinguishes them.

What does a chain line mean on a drawing?

A chain line is a long-short-long pattern used as a centreline. It marks the centre of holes, the axis of cylindrical features, the centre of symmetry of a part, and pitch circles of bolt patterns. The chain line is thin weight. A small cross at the centre of a circle marks the centre of a hole or shaft. Chain lines should start and end with the long stroke, not the short dash.

How do I tell if a drawing is metric or imperial?

Read the title block. AU drawings produced under AS 1100 default to metric (millimetres) and the units may not be explicitly stated. Imperial drawings produced under ASME conventions default to inches with inch marks (") indicating the unit. If a drawing is dual-dimensioned, both metric and imperial values appear (typically with one in parentheses). If a drawing is for an imperial-spec piece of equipment (older US-OEM machinery, agricultural equipment, some automotive components) all dimensions are imperial. When in doubt, look at the diameter of standard fasteners — Ø10 is metric (M10), Ø.375 or 3/8 is imperial.