Basics & process choice
Butt weld vs fillet weld — what's the difference?
Quick answer
A butt weld joins two pieces in the same plane; a fillet weld joins them at an angle (like a T-joint). Fillets are the workhorse of structural fabrication — most welded steel structures are mostly fillets. Butts appear where full-strength, full-penetration joints matter: pipe, pressure, plate splices.
At a glance
| Butt | Fillet | |
|---|---|---|
| Joint shape | same plane | corner/T/lap |
| Typical use | pipe, plate splices | structural steel everywhere |
| Prep | often bevelled + root gap | fit-up and tack |
| Strength path | through-thickness | shear across the throat |