@david6670 Welcome to the TechForum.
The middle number represents the Put-Ups codes from Prysmian Group. I have listed the codes for the part numbers you provided.
18 500 ft Spool
25 500 ft Pull Pac
30 1000 ft Pull Pac
41 1000 ft Reel
46 5000 ft Reel
43 2000 ft Reel
Check out this forum post on the other Put-Ups and color codes.