BearingsAdvantage:Ceramic Engine Bearings with Re-enforced Nylon (Polymite )Cages.This special design can withstand higher load than normall,re-enforced cage can use on higher speed and heavy duty.This 7X19X6 mm Ceramic Ball Bearing designed to be a direct replacement for the front bearing in many .21-.28 Nitro Engines. This bearing is specially designed to withstand high RPMs that exist in this application. This bearing is an open design to allow the oil from the fuel to keep the balls well lubricated. Tips:Diagnosing: If you hold the head of the engine with your hand and a rattle sound dissapears then you have a worn out rear bearing. The risks/issues of a bad rear bearing are not holding a tune, crank can get worn, and worst of all the bearing comes apart and eats your piston/sleeve.Installation: The best way to install is to use a bearing puller/installer, OFNA makes a very affordable one. If you place the new bearing in the freezer for 15 minutes it will be easier to install.Positioning: For proper lubrication, face the open side where you can see the balls to the rear of the motor (not the clutch side).Break In: For the first run of these bearings, We suggests that you fatten your motor up on the high-end needle so the ceramic balls will seat instead of skidding them.Widely used in household appliances, garden machinery, outdoor vehicles, industrial production, etc. Suitable for skateboards, longboards, inline skates, scooters, robots, ship rudder axles, etc.Features: small friction, fast speed, smooth, low noise.