Which of the following screws is designed to join metal components?

• A. Wood screw
• B. Self-drilling screw
• C. Lag screw
• D. Square head bolt

Answer: (B)

The self-drilling screw is specifically designed to join metal components effectively. This type of screw features a unique drill point that allows it to penetrate directly into metal without the need for a pre-drilled hole. The capability to drill its own hole makes it highly suitable for metal-to-metal applications, as it ensures a secure connection while reducing installation time.

In contrast, wood screws are primarily designed for joining wood materials; they often have threads that grip into wood fibers, which wouldn't work effectively with metal. Lag screws, while they can be used in some metal applications due to their high strength, are mostly intended for heavy timber connections or situations where a robust fastening is necessary. Square head bolts are typically used in conjunction with nuts and are more suited for providing a secure hold in various materials, but they don't offer the same ease of installation as self-drilling screws do in metal applications. Thus, the self-drilling screw is the most appropriate choice for joining metal components.