This is an inner thread (outer nut) adapter that will connect to any of our wireless boards or interface cables and allow you to use an antenna/cable that has an outer thread configuration.
You should not need this adapter with any of our antennas or dev boards. These adapters are listed only to help SparkFun users that have rare or odd antenna coupling needs. Be sure to check out the SMA connector tutorial here for more information on SMA connectors.