A reverse-polarized coaxial connector is required by FCC part 15 rules for spread spectrum wireless devices. This type of connector uses a male pin center conductor in a female threaded coupling nut and a female center conductor in a male threaded coupling nut. This arrangement prevents the connector from mating with a standard connector.

The two most common reverse-polarized interfaces are RP-TNC and RP-SMA connectors, shown in the photos below.

Reverse polarized
TNC Plug (male)

Reverse polarized
TNC Jack (female)

Reverse polarized
SMA Plug (male)

Reverse polarized
SMA Jack (female)