Which of the following specifies sizes using a penny system?

The choice that specifies sizes using a penny system is the finishing nail. The penny system is a traditional method of measuring nails where the size of the nail is denoted by the term "penny," which historically originated from the price of 100 nails in England. For example, a "2d" nail is a 2-penny nail, and the "d" stands for denarius, an old Roman coin.

Finishing nails, in particular, are commonly measured this way, allowing users to easily identify the length and suitability of the nails for specific carpentry tasks. While the other options, such as a nail, screw, or bolt, might have their own systems for designation, they typically do not employ the penny system to convey their dimensions in the same prevalent manner that finishing nails do.