Which of the following is a valid type of weld shape?

A fillet weld is indeed a valid type of weld shape, commonly used in various welding applications. The fillet weld is characterized by a triangular cross-section that joins two surfaces together, typically at a right angle. This type of weld is particularly useful in joining metals at corners or edges, providing structural strength and stability to the joint.

Fillet welds can be applied in numerous configurations, making them versatile for both structural and fabrication purposes. They are often used in the construction of steel frames, brackets, and attachments in both light and heavy fabrication contexts.

The other choices, while having significance in different contexts, do not represent valid weld shapes in the same sense as the fillet weld. For example, square and circular might be descriptive of potential geometric forms or design features, but they do not refer to standardized weld shapes recognized in welding practices. Concave, while perhaps descriptive of a profile, is not classified as a specific weld type either. Understanding weld shapes, particularly the significance of the fillet weld, is crucial for interpreting welding drawings and ensuring the appropriate welding processes are employed.