Hoisk,
![Welcome!! :text-welcomeconfetti:](./images/smilies/text/welcomeconfetti.gif)
Welcome to the Mitchell Reel Museum! (MRM).
What you have is what is known as a "Cartridge Spool". These were spools that were originally included in-the-box with a new Mitchell 300 reel as sort of a promotional item in European countries. Some say the first cartridges that came in the reel box, came pre wound with
Starlon fishing line. Later, cartridges were sold separately as an accessory, with
Garcia Bonnyl or
Royal Bonnyl fishing line.
I think what the cartridge system did is provide the owner with a special spindle that allowed you to drop in various cartridges with different types of line. You could then buy a pre-wound cartridge separately spooled with fresh various line diameters. Not having to buy the entire spool assembly, spindle, spool shell, and etc., to get fresh line, costs less and made changing line even more convenient. They even had small plastic spool cases that said MITCHELL CARTRIDGE on the cover instead of LARGE OR SMALL.
Kind Regards,
Bill
P.S. The spring assembly you show in your photo is upside down. The little legs on the spring always go up.
![Laughing :lol:](./images/smilies/icon_lol.gif)