The SMA connector employs a 1/4-inch diameter, 36-thread-per-inch threaded barrel. The male is equipped with a hex nut measuring 5/16 inch (0.3125 inch / 7.9 mm) across opposite flats, thus taking the same wrench as a #6 SAE hex nut.
A standard-polarity SMA male connector has a center pin surrounded by barrel with inside threads, and the standard SMA female connector has a center sleeve surrounded by a barrel with outside threads. As with most other connectors, the gender assignment thus corresponds to the innermost electrical component. There are also reverse-polarity ("RP") SMA connectors in which the pin and sleeve are swapped; so that the "male" RP-SMA has a center sleeve surrounded by an inside-threaded barrel, and the "female" RP-SMA has a center pin and an outside-threaded barrel. See below for a fuller description. [1]
The SMA connector uses a polytetrafluoroethylene (PTFE) dielectric which will contact along the mating plane. Variability in the construction and the mating of the connectors limit the repeatability of the connector impedance. For that reason and that they are just rated for a limited number of connection cycles, an SMA connector is not usually a good choice for metrological applications.[2]
SMA connectors are rated for up to 500 mating cycles,[3] but to achieve this it is necessary to properly torque the connector when making the connection. A 5/16-inch torque wrench is required for this, set to 3–5 in·lbf (0.3 to 0.6 N·m) for brass, and 7–10 in·lbf (0.8 to 1.1 N·m) for stainless steel connectors. Flats are sometimes also provided on the cable side of the connector assembly so that a second wrench can be used to prevent it from rotating and damaging the joint to the cable. It is also advisable to inspect and clean out loose debris from the internal surfaces with compressed air or a gas duster can before mating