When fidget spinners first hit the market and started to gain in popularity, nearly all of them had one type/size of center bearing - a 608 bearing. And if you've looked at spinners online at all you've probably seen many of them using the '608' description in the title of the product.
When it comes to fidget spinner bearings, they are usually categorized by size (which usually has a corresponding number, like 608) and by type (steel, hybrid ceramic, or full ceramic).
Common Sizes of Fidget Spinner Bearings
Overview: Most commonly used bearing for fidget spinners, but also for skateboards, longboards, and inline skates, and kick scooters. 608 bearings are by far the most common standardized ball bearing around. You'll see that many 608 bearings are labeled with an ABEC number. This is a numerical rating for the tolerance or precision of the bearing, where the higher the number the more precision the bearing.
Inner Diameter: 8mm
Outer Diameter: 22mm
Thickness / Width: 7mm
Benefits: They are easy to come by since they are a standardized size and you can find them in a variety of configurations (ie. steel, hybrid ceramic, full ceramic...or sealed and unsealed).
Downsides: Typically require more mass to move them efficiently, so they're commonly found on larger spinners.
Overview: The r188 bearing is growing in popularity and are being used alot more in smaller fidget spinners because of its smaller footprint. The mass to bearing ratio plays a big part in the spin time of a spinner. So generally speaking, if you have 2 spinners with equal mass...1 with a 608 bearing and 1 with a r188 bearing, the r188 bearing spinner will out spin the 608 spinner.
Inner Diameter: 1/4"
Outer Diameter: 1/2"
Thickness / Width: 1/8″ or 3/16"
Benefits: Their smaller size allows them to be fit into smaller spinners and allows for increased spin time.
Downsides: Usually a little tougher to come by since they're not a common. They usually are a bit more unstable while spinning because of their size.
Overview: Not nearly as common as the 608 bearing, but it does look quite similar, and is only slightly different dimensionally.
Inner Diameter: 6mm
Outer Diameter: 17mm
Thickness / Width: 6mm
Benefits: It's smaller size also makes for increased spin durations. Durable construction and comes in a variety of configurations.
Downsides: Much like the r188, they're not as common which makes them a bit more expensive.
Common Types of Fidget Spinner Bearings
This is not an all-encompassing list of the types of ball bearings that exist, but rather a short overview of the most commonly seen bearings for fidget spinners.
Stainless Steel Bearings
Typically found in inexpensive fidget spinners, stainless steel bearings do provide a smooth spin and are relatively quiet. They don't dissipate heat well and heat greatly reduces the spin time. For this reason alone, stainless steel bearings typically make for the slowest spinning spinners.
Hybrid Ceramic Bearings (BEST & MOST DESIRABLE)
Hybrid Ceramic Bearings are the best choice for fidget spinners. They have stainless steel races (outer case and inner ring) and ball bearings made from Silicon Nitride (noted as Si3N4) or Zirconium Dioxide (noted as ZrO2). The blackish-gray balls are Si3N4 and the white balls are ZrO2. Silicon Nitride Si3N4 bearings are the preferred choice as they provide the best potential spin time. The increased performance comes from the ceramic balls ability to resist and dissipate heat. The ball bearings are usually held in place by a retainer (or cage) made of nylon or stainless steel.
Full Ceramic Bearings
Made entirely of ceramic components (Outer and Inner Races, Retainers/Cages, and Balls), full ceramic bearings provide a unique feel when spun in a spinner. The ceramic pieces transfer more of the vibration through to the user, giving the user a much different feeling. Because of their noisier spin and fragility, they are not extremely common or desired in fidget spinners.