This is a hard EVA original economizer for the Ambassador 4600. It is compatible with Ultra Cast Spools (shaft diameter 14mm). By attaching it to the genuine spool, you can create a shallow spool, eliminating the need for backing and reducing weight. The groove is approximately 6mm to the spool edge. Line Capacity: Nylon line: 16lb x 75m 20lb x 60m PE line: 3.5 (varies depending on the manufacturer) x 75m *For safety, double-sided tape is included for installation, but it should not slip once line is wound. (Be careful as it will be difficult to remove if you attach it with the double-sided tape) *There may be slight variations due to being handmade. *Please note that we have not confirmed compatibility with all 4000 series reels. *The reel and spool in the photos are not included.