One of the most important parts on a Rollerskate or Skateboard are the Bearings inside the Wheels.

1. There are two types of Covers on Bearings - Shields and Seals.
2. There are 5 ABEC Ratings - 1, 3, 5, 7 and 9.
3. There are 2 Types of Lube for the Bearings - Oiled, or Greased.
4. Most Wheels take 2 Bearings per Wheel - 8 on a Skateboard or 16 for a Pair of Rollerskates.

Metal Shield Bearing

Rubber Sealed Bearing

• The 2 Different Covers on Bearings have quite an impact on the care and Maintenance as well as the longevity of the Bearing. If you have a Sealed Bearing that would mean the Bearing Cover is Rubber or Neoprene and will keep the Elements out of your Bearings, which can make your bearings last longer, however this will create Drag on the inner raceway if there is any Contact with the Raceways.

• A Shielded Bearing has a metal cover on the Outside of the Bearing and is Attached to the bearing either by a Clip (Serviceable) or is Pressed into the Bearing called a Stake Shield (once removed it cannot be re-installed) and is most Common.  Shields do not keep the elements out as well as a Seal but there is no drag on the Bearing whatsoever making it a Faster Bearing as there is no Contact with the Shield. It is also easier to maintain a Shielded Bearing as you can lubricate the Bearings without having to remove them.
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• There are 5 Abec ratings. An ABEC Rating refers to the Grade of the Bearing in Reference to smoothness and Noise. The quieter the Bearing and the TIGHTER the TOLERANCES between the Radial Ball Run -In and the Run-out - the Higher the Abec Rating. Most Industrial Bearings, such as Grinders - Drills - Routers etc. use Grade Abec-1. An Automotive Manual Transmission would use an Abec 3. Medical equipment might use an ABEC 5. The Rocketship to the Moon might use an ABEC 9 - However Jet Engines in the past have used an Abec 1 High Velocity Bearing. Abec is about Quality of Tolerances and an Abec 7 is not faster than an Abec 1 - What makes a Bearing fast is a lighter weight Lubricant. If you use a lightweight Oil it will dissipate faster than grease and you must remember to RE-OIL your Bearings on a regular Basis - Like every Saturday if you skate everyday or every other saturday if you skate 3 times a week - If the Bearings are loud when they spin, they are dry and you need to oil your Bearings before they disentigrate from friction.
• A Higher Abec Rating does not Refer to Speed.
• Depending on how fast you want your bearings to go you must decide on OIL (The fastest) or GREASE  (The least Maintenance) If you dont keep oil or grease in the Bearings they will run Metal to Metal and will seize from Friction and Heat and break apart. See the guide on Bearing Maintenance.
• All Wheels require Bearings in order to roll well. Almost all wheels including Rollerskates, Rollerblades, Scooters and Skateboards require 2 Bearings - One on the Inside and One on the Outside. Most Wheels have an inner Spacing between the Bearings of .400 on Average for Skateboards and Blades or .325 and .285 for Indoor Rollerskates. Rollerskates can also use a Different Bearing Size (which can also date back to the 60's and 70's on Early Skateboards) you can find imprinted on the cover of a precision Bearing. If you have an 8MM Axle the bearing Number is 608. If you have a 7MM Axle the Bearing Number is a 627.
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