These specs include Shimano's S Concept design, which stresses a smooth, silent operation as well as durability. The S A-RB ball bearings of this reel aid in durability. These ball bearings have been through a treatment process that makes them ten times more resistant to corrosion than traditional ball bearings. These bearings are also shielded on both sides to prevent salt or sand from interrupting their rotation. The cold forged aluminum spool is another feature geared toward durability, as it provides more lasting strength than a diecast aluminum or graphite spool. On the smooth operation side, the Shimano Symetre 4000 FJ has a counter balanced rotor that prevents wobble during the retrieve, a feature Shimano calls Dyna-Balance.
