Note: 326 series wheels cannot be upgraded to Killian bearings. They come with pressed cartridge bearings so they may slide onto 3/4" axles.
Also note: 326 series may be used as free wheels (front or rear) OR as rear drive wheels. There are three holes in the hub (1-7/8" apart on center) where a sprocket or other drive system can be bolted. This is known as a "three prong" system, as opposed to a "keyway" system.