What symbol is used to indicate that a weld is required on all four sides?

The correct symbol that indicates a weld is required on all four sides of an object is represented by a square. In welding symbols, a square signifies that the welding is to be uniformly applied on all four edges of the connected materials. This ensures that the joint has continuity and strength across its full perimeter.

The other symbols mentioned, such as the circle, diamond, and triangle, denote different types of welding specifications and processes, but they do not convey the requirement for welding on all four sides. The square is particularly used in structural applications where complete joint penetration or reinforcement for load-bearing purposes is necessary, which is why it is essential to recognize its significance in the context of welding symbols. Understanding these symbols is crucial for those in the contracting field to ensure that projects are executed with the correct specifications.