Square butt weld
Applied to joint
Butt joint — plates aligned end to end
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Equipment for groove welds
MIG and TIG machines suited for groove weld preparations on plate.
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Description
A butt weld with no groove preparation on either member. The joint faces are left square (unprepared). Full penetration is assumed unless a partial penetration depth is dimensioned. Suitable for thinner materials where full fusion can be achieved without a groove.
In plain English
The simplest groove weld -- you just butt the two pieces together with no bevel or prep and weld straight into the square edge. Works well on thin sheet and plate up to about 5-6 mm. Above that, you struggle to get full penetration without a root gap or backing. If you see two parallel vertical lines on the symbol, that is your square butt.
Symbol position
On the reference line, arrow side or other side depending on joint orientation.
Size notation
Depth of penetration (S) shown to the left of the symbol if partial penetration. Root gap shown inside the symbol or in the tail.
Common uses
- Thin sheet metal joints (up to ~6 mm)
- Pipe root passes before filling with a V prep
- Light structural sections
- Tack welds and temporary joints
