Which type of bolt is useful when attaching metal to wood?

The carriage bolt is specifically designed for situations where metal needs to be fastened to wood. Its unique features include a rounded head and a square section directly beneath it, which helps to prevent the bolt from turning when the nut is tightened. This design is particularly beneficial when working with wood, as it allows for a secure fit without the need for a wrench on the top side, making installation easier and more effective.

On the other hand, while hex bolts and machine bolts can also be useful in various fastening tasks, they are generally better suited for all-metal connections or situations where access to both sides of the assembly is available. An eyebolt is intended for lifting or securing items and is not designed for general fastening purposes like connecting metal to wood. Therefore, the carriage bolt stands out as the most effective option for this particular application.