The difference between these two kits is that the # HSE7K-TR1 comes with a complete hub and rotor that replaces your existing hub, where the # HSE7K-TR1SO is only the rotor which slips over your existing hubs. The hub that is included with the # HSE7K-TR1 requires that your current hubs use inner bearing # 25580 and outer bearing # 14125A, so if your hubs have different bearings using the rotor only kit would be the best option. You will want to confirm that you've already got idler hubs... view full answer...