For light materials the square-edge butt joint is the very easiest to make and can be welded without filler rod. Butt Joint consists of “butting” two pieces of metal up against one another and then welding along the seam between them. If the weld is to be made
without filler rod, excessive care must be taken to avoid burning through the metal.

The single-V butt joint is favorable on material ranging in thickness from 3/8″ to 1/2″ in order to safe complete penetration. It is prepared like a regular butt joint other than that the top edge of each piece is chamfered in order to reduced the area of contact between the two. The included angle of the V formed by the chamfering should be approximately 60° with a depth of about 1/8″ to 1/4″.

The double-V butt joint is needed when the metal exceeds 1/2″ thickness and the design is such that the weld can be made on both sides. This is like a single-V joint except that both the top and the bottom edges of the pieces are chamfered, and welding is performed on both sides. With a double V there is greater assurance that diffusion will be complete.