HIPA Pack of 5 Big Snap in Primer Bulb # A056013 for MTD Troy-Bilt 704r 705r 750r 775r TB10CS TB15CS TB20CS TB25CS Gas Trimmer Replacement manufacturer part number: A056013 791-683974B 683974B 224242-02 Note: The primer bulb is larger than 188-512 The base of the primer bulb diameter is 1-inch / 25.4mm, while wlabro 188-512 bulb base diameter is 21.5mm Please check your old primer bulb size caefully before purchase