Spacers: The metal or plastic tubes that go between the bearings Axles: The long bolts that go through your wheel, bearings and spacers.

Diameter - The length of a straight line through the center of an object from side to side; width; thickness. Measures the width. Often measured in millimeters. (i.e. 80mm)

Durameter - A measurement of the hardness or softness of a wheels urethane (rubber). 78a would be soft and 100a would be hard. Softer grips better, but wears out quicker. Harder lasts a long time, but does not grip as well.

608 - a number which refers to diameter and specs of a wheel hub or bearing size. A "608" bearing or wheel is standard size. Most everything in the skate industry is a "608."

688 - a number which refers to diameter and specs of a wheel hub or bearing size. A "688" bearing or wheel is MICRO size. When buying wheels or bearings everything must fit together. A "688" bearing fits a "688" hub wheel.

Rebound - how fast a wheel bounces back or responds to your movements. Usually the more expensive the wheel, the better rebound you have. Pick a inline wheel up and bounce it on the floor. This is a good indication of the "rebound".

Anti-Rocker - A special type of wheel for aggressive skating. This wheel is always smaller than all other wheels. ranges from 46mm - 50mm. These wheel are also very hard. An anti-rocker wheel is used in the middle of the skate. 2 anti-rocker wheels in the center and usually 2 regular size wheels on the ends. Anti-rocker setups help with street skating and grinding. You can slide on them easier. They are not recommended for huge gaps or stairs.

Hi-Lo - A configuration of the wheels on a skate. Usually inolves 2 larger wheels in the back and 2 smaller wheels in the front. Usually found on race skates and Hockey skates. Great for quick starts!