How to read a square groove weld symbol — root opening, why groove depth does not apply, and D1.1:2025 CJP thickness limits by welding process.
Square Groove Weld Symbol — Anatomy
CJP — R=1/8" inside
PJP — (3/8) weld size
Double square groove
Key rule: Square groove welds have no groove depth (D) per A2.4 §7.2.6. The groove faces are parallel — there is no angled preparation to measure. Only root opening (R) and weld size (S) apply.
D1.1:2025 Figure 5.1
Prequalified CJP Thickness Limits
Square groove CJP is prequalified only for thin material. For thicker plate, switch to a V-groove or bevel groove.
Process
Designation
Max Thickness
Root Opening
Notes
SMAW
B-L1a
1/4"
R = T1
With backing
SMAW
B-L1b
1/4"
R = T1/2
Backgouge + backweld
GMAW/FCAW
B-L1a-GF
3/8"
R = T1
With backing
GMAW/FCAW
B-L1b-GF
3/8"
R = 0 to 1/8"
Backgouge + backweld
SAW
B-L1-S
3/8"
R = 0
Flat only
SAW
B-L1a-S
5/8"
R = 0
Flat, with backgouge
Common error: Specifying a square groove CJP on 3/8" plate with SMAW. The prequalified limit for SMAW is 1/4" — using 3/8" plate requires either switching to GMAW/FCAW or changing the joint to a V-groove or bevel groove.
Reading the Symbol
How to Read Square Groove Dimensions
Root opening (R) goes inside the symbol — between the two vertical parallel lines. For the B-L1a prequalified joint, R equals the material thickness (R = T1). If no root opening is shown and the symbol just displays two vertical lines with no dimension inside, the symbol is incomplete.
Weld size (S) in parentheses to the LEFT — PJP only. Square groove PJP has no thickness limit because you are specifying the effective weld size directly.
No groove depth (D) — per A2.4 §7.2.6, this concept does not apply to square groove welds. Writing 1/4 (3/8) || is incorrect; it should be (3/8) || with root opening inside the symbol if needed.
Common Questions
Square Groove Weld Symbol FAQ
What is a square groove weld symbol?
A square groove weld symbol consists of two short vertical parallel lines perpendicular to the reference line. It represents a joint where both members have square (flat, unprepared) edges. It is the simplest groove weld type. Per AWS A2.4 §7.2.6, groove depth (D) does not apply to square groove welds — the only dimensions are root opening (inside the symbol) and weld size in parentheses for PJP.
What is the maximum thickness for a square groove CJP?
Per D1.1:2025 Figure 5.1, square groove CJP is prequalified only for thin material: SMAW — 1/4 inch maximum, GMAW/FCAW — 3/8 inch maximum, SAW — 3/8 to 5/8 inch (flat position only). For thicker material, a V-groove or bevel groove is required. Square groove PJP has no thickness limit because the weld size (S) is specified separately.
Why does groove depth not apply to square groove welds?
Per AWS A2.4 §7.2.6, groove depth (D) is not applicable to square groove welds because the groove faces are parallel — there is no angled preparation to measure a depth against. The weld either penetrates the full joint thickness (CJP) or to a specified weld size (PJP). The only relevant dimensions are root opening (R) placed inside the symbol and weld size (S) in parentheses to the left for PJP.
What is the root opening for a square groove weld?
Per D1.1:2025 Figure 5.1, the root opening for prequalified square groove CJP butt joints varies by joint type: B-L1a (with backing) requires R equal to the material thickness (R = T1). B-L1b (with backgouge) requires R = T1/2 for SMAW or R = 0 to 1/8 inch for GMAW/FCAW. SAW joints (B-L1-S) use R = 0. The root opening is placed inside the square groove symbol between the two vertical lines.