Which of the following statements is true regarding double head nails?

Double head nails, also known as duplex nails, are specifically designed for temporary fastening applications, making the option regarding their usefulness for temporary form connections correct. The two heads allow for easy removal after the formwork is no longer needed, making it convenient for situations where a structure needs to be held in place temporarily, such as in concrete formwork or scaffolding.

In contrast, double head nails are not typically used for permanent fastening because their design allows for removal; therefore, they wouldn't be suitable where a lasting hold is required. Additionally, they are not preferred for heavy framing, as heavier structural work might require a more robust fastening solution, such as ordinary nails or screws that offer a stronger grip. The mention of a single head does not apply here, as double head nails specifically feature two heads for the ease of pulling out the nails after their temporary function is served.