A reverse-polarity 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-polarity interfaces are RP-TNC and RP-SMA connectors, shown in the photos below.

Reverse polarity
TNC Plug (male)

Reverse polarity
TNC Jack (female)

Reverse polarity
SMA Plug (male)

Reverse polarity
SMA Jack (female)