Which type of nails have two heads, one lower than the other, and are used for temporary construction?

Double-headed nails are specifically designed for temporary construction purposes, which is why they are the correct choice. These nails feature two heads: a lower head for driving into the material and a second, upper head that remains exposed after the nail has been driven in. This design allows for easy removal of the nail after the temporary structure is no longer needed.

In construction, temporary frameworks or structures often require materials to be easily dismantled, and double-headed nails fit this need perfectly. The upper head gives workers a point of leverage for pulling the nails back out without damaging the surrounding materials.

Other types of nails, like common nails or brads and finishing nails, are not designed for this purpose. Common nails are meant for permanent fastening and do not have the same removable feature. Brads and finishing nails are thinner and typically used for trim work, where aesthetics are more important than the ease of removal. Spikes are larger, heavy-duty fasteners used in specific applications like railway or heavy timber work and also do not have the dual-head feature necessary for temporary projects.