SAN-O bearings are specially designed as "Turning Bearings".
These babys feature polished chrome balls, nylon cages 10.3 mm spacers and the very best synthetic bearing grease from Japan. These are not considered "Speed Bearings" but they still get you going plenty fast. It may be a bit counter-intuitive but we've found that this setup is far superior for making sweeping, carvy turns... smoothly and quietly.
Why 10.3 mm SPACERS rather than built-in SPACERS?
We've been using built-in type bearings since 2006... We bought-into the "Sloppy 7" story line which basically asserted that stacking tolerances was bad for speed. And that's still probably true, but Hamboards are about graceful turning not just speed. We have come to suspect that during repeated big heavy turns, like with a Hamboard, the built-in spacer type bearings are so precisely mated that they tend to apply intense side loads to the bearing components and alternatively push-out the inside bearings, eventually loosening both bearings from their snug fit in the wheel hubs. It makes sense because when any system is loaded, it deflects. It's super hard to see with the naked eye, but it happens. Repeated alternating deflection leads to wear and fatigue. This fatigue eventually results in bearing vibration (noise) and friction (drag). Built-in spacer bearings are awesome for lots of uses... especially for straight-away speed... but maybe not so great for big heavy turning like on a Hamboard or cruiser.
The SAN-O bearing 10.3 mm spacers give extra tolerance gap to help manage the tremendous side load deflections without wearing the bearings guts as much and without pushing-out the inside bearings as much... We think that the result is that SAN-O bearings handle turning better and they stay locked in the plastic wheel hubs better than built-in type bearings.
WHY SYNTHETIC GREASE rather than OIL?
Grease bearings aren't any where near as commonly available as "Speed Bearings". It's no secret that bearing manufacturers think that consumers assume that "More Speed" is "More Better" all the time. That's definitely true if you're going straight, but not necessarily for a Hamboard that's screaming to turn.
Grease is thicker and more viscous than oil, which sounds like "drag". Engineers know that grease (rather than oil) is a superior lubricant for low and moderate speeds. (There's oil in your car engine that rotates ten-thousands of times a minute, but grease in the entire drive train which rotates hundreds of times a minute.) There are all types of bearing grease out there, but specifically formulated synthetic bearing grease is vastly superior to oil based grease because of the very narrow molecular weight distribution (polymer physics "mumbojumbo"). We've found the bearing grease winner and it's specially formulated for ball bearings. When this grease warms-up just a little bit it gives a buttery carve that really lasts.
Bearings aren't all that expensive, so we might as well use our brains and build the best for Hamboards. That's what SAN-O bearings are... the very best. We hope you like them!