SMA connector

SMA (SubMiniature version A) connectors are semi-precision coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw type coupling mechanism. The connector has a 50 Ω impedance. SMA is designed for use from DC to 18 GHz, but is most commonly encountered with WiFi antenna systems and USB Software Defined Radio dongles.

SMA connectors can be visually confused with the standard household 75 ohm Type F Coax Connector (diameters: Male 7⁄16 in (11 mm) circular or hex; Female 3⁄8 in (9.5 mm) external threads), as there is only about a 2 mm difference overall in the specifications. Type F cannot be mated with SMA. Of course, this connection is possible using an adapter.

Connector design

The SMA connector employs a 1/4 inch, 36 thread. The male is equipped with a 5/16 inch (0.312 inch) hex nut. This is not to be confused with a hex nut that accommodates a screw/bolt with 5/16 inch nominal outer diameter. This would result in an SMA connector that has larger minimum cross section dimensions than 5/16 inch. Instead, the dimensions of the SMA connector are such that the width across the flats is 5/16 inch. This is the same as the #6 SAE hex nut. Thus, the SMA connector requires a 5/16 inch wrench to fit across the flats. A 5/16 inch hex nut would require a 1/2 inch wrench to fit across the flats.