Steel shop drawings use a compact shorthand: member callouts like W250x45 or HSS 152x152x9.5, elevation notes like TOS, side notes like NS, FS and BS, bolt and hole notes like SSL or SC, and weld notes like CJP. Most of these abbreviations are shared across Canadian and US steel detailing, but none of them are law. The legend and general notes on the drawing set always govern for that project.
This post is a working legend for contractors, builders and site supervisors who have a steel shop drawing in front of them. If you need the bigger picture of how a drawing set is laid out, start with our guide on how to read structural steel drawings. For concrete reinforcement shorthand, see the separate rebar shop drawing abbreviations legend.
How a steel member callout is put together
A member callout tells you the shape, the size and often the weight. In Canada callouts are metric: depth or outside dimensions in millimetres and mass in kilograms per metre.
| Callout | Shape | How to read it |
|---|---|---|
| W250x45 | Wide flange beam or column | Nominal depth 250 mm, about 45 kg/m |
| HSS 152x152x9.5 | Square hollow structural section | 152 mm by 152 mm outside, 9.5 mm wall |
| HSS 168x6.4 | Round HSS | 168 mm outside diameter, 6.4 mm wall |
| L102x76x9.5 | Angle | Legs of 102 mm and 76 mm, 9.5 mm thick |
| C200x17 | Channel | 200 mm deep, about 17 kg/m |
| PL 12x200 | Plate | 12 mm thick, 200 mm wide (length given separately) |
| FB 10x75 | Flat bar | 10 mm thick, 75 mm wide |
| RD 20 | Round bar | 20 mm diameter solid round |
Where you see W8x18 or similar, the drawing is using the imperial designation for the same family of shapes (inches of nominal depth and pounds per foot) rather than the metric one.
Material grade usually sits in the general notes rather than on every callout, for example "W shapes to CSA G40.21 350W" or "HSS to 350W Class C". If a piece needs a different grade, the shop drawing calls it out on that piece.
Members, shapes and parts
These abbreviations name the pieces themselves.
| Abbreviation | Meaning |
|---|---|
| W | Wide flange shape |
| HSS | Hollow structural section (square, rectangular or round tube) |
| L | Angle |
| C, MC | Channel, miscellaneous channel |
| WT | Tee cut from a W shape |
| PL | Plate |
| FB or FL | Flat bar |
| RD | Round bar |
| SQ | Square bar |
| CHK PL | Checker (tread) plate |
| BM | Beam |
| COL | Column |
| BR | Brace |
| BP | Base plate |
| CP | Cap plate |
| EP | End plate |
| GP or GUS | Gusset plate |
| STIFF | Stiffener |
| SPL | Splice or splice plate |
| AB | Anchor bolt (anchor rod) |
| EMB | Embedded plate or embed |
| LLV, LLH | Long leg vertical, long leg horizontal (how an unequal angle is oriented) |
LLV and LLH matter more than they look. An unequal angle lintel installed with the wrong leg vertical is noticeably weaker, which is why detailers call it out on every angle piece.
Elevations, location and geometry
| Abbreviation | Meaning |
|---|---|
| TOS | Top of steel |
| BOS | Bottom of steel |
| TOC | Top of concrete |
| TOG | Top of grout |
| EL or ELEV | Elevation |
| CL or ℄ | Centreline |
| WP | Work point, the reference point dimensions are measured from |
| GL | Grid line |
| c/c or O.C. | Centre to centre, on centre |
| CLR | Clear (a clear distance between faces) |
| NS, FS, BS | Near side, far side, both sides |
| ES | Each side |
| EQ | Equal (spaces are equal) |
| TYP | Typical (applies to all similar locations) |
| SIM | Similar (same idea, check dimensions) |
| OPP | Opposite (mirror image) |
| THK | Thickness |
| LG | Length |
| R | Radius |
| Ø or DIA | Diameter |
The difference between TYP and SIM trips people up. Typical means the same detail repeats. Similar means the concept repeats but sizes or dimensions may change, so you still read the dimensions at each location.
Bolts and holes
Bolt notes normally give quantity, diameter, grade and the type of connection, and hole notes give the hole type.
| Abbreviation | Meaning |
|---|---|
| HSB | High strength bolt |
| A325, A490 | Structural bolt grades (now grouped under ASTM F3125) |
| TC | Tension control bolt (twist-off type) |
| DTI | Direct tension indicator washer |
| N, X | Threads included in, or excluded from, the shear plane |
| ST | Snug tight |
| PT | Pretensioned |
| SC | Slip critical |
| STD | Standard hole |
| OVS | Oversize hole |
| SSL | Short slotted hole |
| LSL | Long slotted hole |
| GA | Gauge (distance between bolt lines across a member) |
| P or PITCH | Spacing of bolts along a line |
| ED | Edge distance |
Whether bolts are snug tight, pretensioned or slip critical is an engineering decision, not a shop preference. It changes the installation and inspection on site. Your engineer's general notes say which applies where.
Welds and weld symbols
Welds are shown with the standard welding symbol: an arrow pointing at the joint, a horizontal reference line, the weld symbol itself (a triangle for a fillet weld, other shapes for groove welds) and the size and length beside it. A small flag at the junction means a field weld, and a circle means weld all around. Our guide on how to read structural weld symbols walks through them in detail.
The abbreviations that travel with weld symbols:
| Abbreviation | Meaning |
|---|---|
| FW | Fillet weld (on some sets, field weld; check the legend) |
| CJP | Complete joint penetration groove weld |
| PJP | Partial joint penetration groove weld |
| WAA | Weld all around |
| FLD | Field (made on site) |
| SHOP | Made in the fabrication shop |
| E49XX | Electrode classification, the metric counterpart of E70XX |
| NDT | Nondestructive testing (UT, MT, RT, VT) |
| UT, MT, RT, VT | Ultrasonic, magnetic particle, radiographic and visual testing |
The difference between a fillet weld and a groove weld, and how size is measured on each, is covered in our post on structural weld types and sizes.
Finishes, coatings and fabrication notes
| Abbreviation | Meaning |
|---|---|
| PR or PRM | Shop primer |
| NP | No paint (for example on faying surfaces or areas to be fireproofed) |
| GALV or HDG | Hot dip galvanized |
| SB | Sandblast or blast clean |
| CMB | Camber |
| COPE | Cut away the flange to clear another member |
| GR | Grade, or grind, depending on context |
| MK | Piece mark |
| QTY or PCS | Quantity, pieces |
| c/w | Complete with (common on Canadian drawings, as in "beam c/w end plates") |
NP on a beam flange is easy to miss and matters on site. It usually marks a slip critical faying surface or a surface that will receive fireproofing, where shop primer would cause problems.
Drawing and project terms
| Abbreviation | Meaning |
|---|---|
| EOR | Engineer of record |
| IFC | Issued for construction |
| RFI | Request for information |
| REV | Revision |
| UNO or U.N.O. | Unless noted otherwise |
| NTS | Not to scale |
| VIF or FV | Verify in field, field verify |
| NIC | Not in contract |
| BY OTHERS | Supplied or done by another trade |
| DWG | Drawing |
| DET | Detail |
| SECT | Section |
| REF | Reference (dimension or drawing for information only) |
VIF and BY OTHERS are the two to check before you sign off. VIF dimensions have to be measured on site before the piece can be fabricated, and BY OTHERS marks a scope boundary between trades.
Common symbols on steel drawings
Beyond letters, steel drawings use a handful of graphic symbols:
- Grid bubbles: circles at the ends of grid lines with letters one way and numbers the other. Every location on the framing plan is tied to them.
- Section cuts: a line with arrows and a bubble showing the section number and the sheet it appears on.
- Detail callouts: a circle or cloud around an area with a bubble pointing to an enlarged detail.
- Elevation markers: a triangle or target symbol giving TOS or other elevations.
- Revision clouds and triangles: a cloud around changed content and a triangle with the revision number.
- Centreline symbol: a C overlaid with an L, marking the centre of a member or hole group.
- Break lines: a zigzag showing a long member drawn shorter than its true length.
- Piece marks: the label that ties a shop drawing to the erection drawing and to the mark painted on the steel.
What does RD mean on steel shop drawings?
On a steel shop or fabrication drawing, RD means round, almost always a solid round bar called out by diameter (RD 20, or 20 RD). You see it on anchor rods, sag rods, hangers, handrail infill and pins.
The same two letters cause confusion because architectural and plumbing drawings use RD for roof drain. If an RD note appears near a roof opening or on a mechanical coordination sheet, it probably means the drain, not a bar. When the context is unclear, check the drawing's legend or ask the detailer through an RFI rather than guessing.
When an abbreviation is not on the list
Detailers and design offices have their own habits, and some letters mean different things in different sets (GR, FW and ST are the usual suspects). The fix is simple:
- Check the legend and general notes on the first sheets of the set.
- Look at how the abbreviation is used elsewhere on the same drawing.
- If it is still unclear, send an RFI before fabrication or installation. Ten minutes of clarification costs far less than a piece made wrong.
If you are reviewing a set, our checklist on what to include in a steel shop drawing shows what a complete sheet should contain.
Shop drawings that are easy to read
We prepare shop drawings in-house for the structural steel we fabricate, with clear piece marks and notes so every piece is marked to match the drawings and goes up cleanly on site. If you have structural or architectural drawings for a beam, post, lintel or full frame, send them to us for a free take-off and quote, or see our fabrication and detailing services.
Frequently asked questions
What does RD mean on steel shop drawings?
On a steel shop drawing RD almost always means round, as in round bar (for example RD 20 for a 20 mm round bar). On architectural or plumbing sheets the same letters often mean roof drain, so check the drawing's own legend if the context is unclear.
What does TOS mean on a steel drawing?
TOS means top of steel, the elevation of the top of a beam or member. It is usually written with a number, such as TOS EL 100.250, and is the main elevation the shop and erector work from.
What do NS, FS and BS mean on shop drawings?
Near side, far side and both sides. They tell the shop which face of a member a plate, hole pattern or weld goes on, as seen in the view where the note appears.
What does UNO mean on a drawing?
Unless noted otherwise. A note such as 'all welds 6 mm fillet UNO' sets a default that applies everywhere except where a detail shows something different.
Are steel detailing abbreviations standardized in Canada?
Many are used consistently across North America, but there is no single mandatory list. Every good drawing set includes a legend or general notes, and that legend governs for that project.
