The number 320G we find on LCN Door Closers is just a sticker or stamping we find on many of there closers.   The sticker or stamping usually says Listed Door Closer Arm 320 G.  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 803H, 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, 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 (see diagram below).  One of the easiest ways is to match up your door closer on our “Door Closer Information” web page.

The above image shows how to hand a door closer

LCN Door Closers
Norton Door Closers
International Door Closers
Yale Door Closers