UL 94V-0. J300 Series/J320 Headers. These J300 Series/J320 5.08mm pitch PCB headers mate with J-FAT spring terminal connectors, stock number ; 707-8984 707-8984 typical. The JST J300/J320 series Connectors are available in both wire-to-board and wire-to-wire connection. The J300 Connectors feature a double-spring construction consisting of the main spring and a contact pressure adjustment spring. Features ; Benefits. Double spring construction. Housing lances. Secure locking method. Both contact and application tools have identification marks to prevent incorrect combinations. Polarization is achieved by selecting corresponding Key Codes X or Y as shown in the manufacturers part number (e.g. ****-***** -**Y * ) Wire sizes are 14-28 AWG