This is the RAM cradle for the Garmin GPSMAP 60C series GPSs. The GPS snaps securely into the cradle and requires a firm push on the release button. You need the "button" supplied with your Garmin 60-series unit belt clip kit. This cradle is designed to attach to a RAM Diamond Base, part number GRAD, which has the ball required for use in a RAM mounting system.
You may need this part if you are building a custom mounting system for your GPS 60C, or if you have a RAM mounting system for another GPS and need to mount a 60C series GPS.