Which of the following is not a type of nail?

The correct choice is the one that identifies "Allen" as not being a type of nail. In the context of carpentry and construction, nails are categorized based on their intended use and design, with types like finish nails, ring-shank nails, and box nails all serving specific functions in joining wood and other materials.

Finish nails are characterized by their small heads and smooth shanks, allowing them to be driven into the wood and then countersunk for a flush finish, typically used in trim work or cabinetry. Ring-shank nails are designed with ridges along the shank, providing enhanced holding power by creating resistance against pull-out forces, making them ideal for structural applications where a stronger grip is needed. Box nails, similar to common nails but with a thinner shank and a larger head, are often used for light construction and framing due to their ability to hold boards together without splitting them.

In contrast, "Allen" refers to an entirely different context—specifically, it is often associated with an Allen wrench or hex key, which is used to drive bolts and screws with hexagonal sockets. Thus, an "Allen" does not relate to types of nails used in carpentry or construction, making it the correct answer for the question.