The number R6684 we find on Door Closers is just a sticker or stamping we find on many of there closers.   But it is probably an International Door Closer. The sticker or stamping usually says Listed Door Closer R6684.  This is the UL number, which is a testing laboratory.   UL stands for Underwriters Laboratory, which started in 1894, to test electrically and fire equipment.  It does not tell us which door closer you have, but it narrows it down.   Another number we find on closers is 149A and 320 G, which are also UL numbers.  The best way to proceed is to find out as much as you can about the door closer you have.  I would look for Manufacturer (LCN, Norton, Yale, International, Sargent, ect..), possibly a model number,  the hole spacing of the hydraulic cylinder (3/4″ x 9-1/16″, 3/4″ x 8-3/16″, ect…),   how the door closer is mounted (on the door, top jamb, push side, pull side), and the hand of the door .  One of the easiest ways is to match up your door closer is to visit on our “Door Closer Information” web page.  Or visit our International Door Closer section of our website.