MCX (micro coaxial) connectors are coaxial RF connectors developed in the 1980s. They have the same inner contact and insulator dimensions as the SMB connector but are 30% smaller. MCX is standardized in European CECC 22220.
This type of connector is used on the Apple Airport Extreme Base Station's external antenna port and requires an adapter for most antennas. MCX and the smaller MMCX connector are frequently used to connect external antennas to GPS receivers. They are also common on USB DVB-T tuners for computers and laptops, to connect an external antenna to the tuner.
The outer diameter of the plug is approx 3.6 mm or 0.140 inch.