You need 8 wheels for a pair of roller skates (2 x 4 packs or 1 x 8 pack)

OX – PANTHER – MUSTANG – LEOPARD Professional FreeStyle Wheels

Hardness:  Fox (Green) 92A – Panther (White) 95A – Mustang (Gray) 97A – Leopard (Yellow) 99A
Diameter:  57mm
Compound:  Cast Urethane BiCompound Formula
Hub Info:  Shockproof Hub, Green, White, Gray, Yellow

Sold in sets of 8 wheels. No mixing of hardnesses

The Professional (Animals) Wheels are the Tightest of the hi-end Professional FreeStyle Wheels available from Roll-Line today and this series is probably Skated on, Jumped on, and Spun on by more National and World Champions than any other FreeStyle series of wheels. Roll-Line has developed this wheel giving it properties that withstand the extreme abuse a FreeStyle skater can dish out. The Roll-Line Professional is a Lo- Profile, very durable wheel which has incorporated a Hub which is Strong, Light, and with extremely Close Tolerances for Roundness, Trueness, and for the Cage where the Bearings and Spacers are mounted. The Roll-Line Tread is a Cast Urethane BiCompound Formula, which provides very Tight Grip, while providing great ROLL. The hub color identifies which hardness the wheel is.
Green Hub:      92A.
White Hub:      95A.
Gray Hub:        97A.
Yellow Hub:     99A.

The softer the wheel, or lower Shore “A” hardness number, the more the grip and slightly less roll. The harder the wheel, or higher Shore “A” number, the more the roll, with slightly less grip.

Fox – Extra soft, for very slippery surfaces
Panther – Soft, for fairly slippery surfaces
Mustang – Medium, for medium rough surfaces
Leopard – Hard, for rough surfaces

It is almost always recommended to use spacers in the wheels, when using standard 7mm bearings. Long ago, before the use of Lock Nuts (the nuts that have the Nylon Plastic inserts) to hold the wheels on the axles, Jam Nuts were used, but when the spacer was not as wide as the web of the wheel, or the wheel was not machined accurately, the bearings would lock up, the nut had to be tight, and could not be “backed-off”. This method, of locking the Axle Nut down, did promote proper bearing alignment and did increase the diameter of the axle from 7mm to approximately 14mm, because everything was locked down, which also saved the problems of bent axles. Today we do use Lock Nuts. It is still very advisable to lock everything down (especially for FreeStyle, Jam, and Roller Derby Skaters). Roll-Line does provide Spacers for Roll-Line Wheels with each pair of Frames or they can be purchased separately. Properly locking the Wheels down when using standard bearing types, will also promote longer bearing life.
The new Roll-Line 7mm MicroBearing System , provides an absolutely Incredible ROLL (significantly more roll than even the old Snyder Super Fafnir bearings, which used to be the best). The Roll-Line MicroBearing System fits ONLY Roll-Line Frames and DO NOT Require or Use Spacers between the bearings. These MicroBearings are mounted like standard bearings with the shields to the Outside.