Wheel bearings typically fail from water and dirt contamination. The All Balls Front Wheel Bearing Kit was developed in partnership with KML Bearing and is designed for the difficult operating environment of the powersport industry.
Kit contains 1 ball bearing required to re-fit a wheel.
Premium EMQ quality, high-speed bearing featuring low drag, double-lip rubber seals which provide superior exclusion of water, dirt and improved grease retention.
Type TC Nitrile Elastomer wheel seals are specifically designed to keep out water and dirt.
Rubber coated outside diameter creates an optimum seal at hub.
Steel garter spring guarantees constant pressure on the axle shaft over the life of the seal.
These would actually be the bearings housed inside the front knuckles on that 1998 Honda Forman 400. From what I can tell you will have to order the OEM Front Differential Bearings for your ATV.
(OEM Link: http://www.motosport.com/utility/oem-parts/HONDA/1998/TRX400-FOREMAN-4X4/FRONT-FINAL-GEAR-95_01 )
The 2003 Grizzly 660 does not actually have separate wheel bearing seals. Once you pull it apart you can verify there are no seals in there. Also you can take a look at the OEM parts fiche to verify there aren't any seals there here: http://www.motosport.com/utility/oem-parts/YAMAHA/2003/GRIZZLY-660-4X4/REAR-WHEEL