The '/4' indicates pin contacts, general purpose, class G, crimp type. The '-3' specifies shell size 3, which corresponds to 25 contacts. The 'F' suffix indicates a cadmium finish for connectors manufactured after July 1, 1987. This is the military specification number for D-Subminiature connectors, identifying "Connectors, Electric, Rectangular, Nonenvironmental, Miniature, Polarized Shell, Rack and Panel, General Specification for".