Used Cocker Plug IVG Mainspring, 1 and 5/8 inches. One included. This size is too short for most nelson based pumps and is specifically for Autocockers that are pre 98 and lack the internal threaded of the back lower tube. On these Autococker you would used a plug Internal velocity govenor which sits further forward than the screw IVG that is on post 98 autococker. With the longer plug IVG you will need a shorter mainspring that is roughtly 1 and 5/8 inches long. One included. Multiples available, one included, all differ slightly. Various tensions, no color, some light, some hard