Weld Symbol Conventions (AWS A2.4)
Weld symbols follow AWS A2.4. The reference line is a horizontal line; the arrow points to the joint. Information below the reference line applies to the arrow side; above applies to the other side. The weld type symbol appears on the reference line (fillet weld is a triangle, groove weld is a gap between lines, plug weld is a circle). Weld size appears to the left of the symbol; weld length to the right. A circle at the reference line junction means 'weld all around'; a flag symbol means 'field weld.' AWS D1.1 Table 4.5 governs minimum weld sizes by base metal thickness.
Bolt Callout Conventions
Bolt callouts specify diameter, grade, installation method, and sometimes the bolt standard.
- Diameter: 3/4", 7/8", 1" — stated before the grade
- Grade: A325 (medium-strength structural), A490 (high-strength), A307 (low-strength, non-structural)
- Installation method: -N (bearing, no thread exclusion), -X (bearing, threads excluded from shear plane), -SC (slip-critical)
- Tension-control (TC) bolts: specified by drawing note when TC installation method is required
- Galvanized bolts: specified separately; A325 galvanized are F1852 TC bolts in most current practice
Common Misreads and How to Avoid Them
The most common misread is treating 'Approved as Noted' review comments as engineering approval of every weld and bolt shown. The EOR may have flagged a specific weld as undersized in a review comment — that comment governs, not the original drawing. Always read the full set of review comments when working from an 'Approved as Noted' package. The second most common error: reading weld length as weld spacing. A callout of '1/4 F 6-12' means a 1/4" fillet weld, 6" long, at 12" spacing — not a 6" and 12" alternating pattern.