The 1000, with a 5.2:1 gear ratio, is designed for light-duty applications. The 2000, 2500, and 3000 have a 6.0:1 gear ratio, with varying capacities.
The spool features a guide strip for the braided line, and the slow S-Curve oscillation system ensures even line winding. The drag system combines carbon and stainless steel discs. The 2000 size also features 10+1 bearings. To decide between two sizes, compare how well they balance with your rod and the required line capacity.