Final answer:
The physical structure of a male coupling can be identified by the lugs on the shank, which are protrusions that ensure a proper connection with a female coupling.
Step-by-step explanation:
One way to identify the physical structure of a male coupling is by the lugs on the shank. These lugs are protrusions that can be found on the external part of the male coupling's shank, which is the section of the coupling that inserts into a female coupling. The presence, shape, and arrangement of these lugs are often unique to the type of coupling and are used to help align and secure the connection between the male and female parts. While other features such as the swivel protector, coating, and shank length also contribute to a coupling's characteristics, the lugs are specifically designed to ensure a firm and proper connection, thus distinguishing one type of coupling from another.