Devil 57mm Freestyle Wheels

The RollLine Devil 57mm small profile width professional freestyle wheels are designed to be used on many types of extremely slippery skating surfaces including standard wood floors coated with plastic or polyurethane, as well as unusual surfaces like tile basketball and volleyball courts, Indoor or outdoor tennis courts and concrete or terrazzo surfaces. Devil wheels utilize a stiff Delrin hub which is strong, light, and with close tolerances for roundness, trueness, and for the cage where the bearings and spacers are mounted. They also have a higher rebound than most other RollLine thermoplastic and urethane wheels (except the Helium wheels). 
The tread color identifies which hardness the wheels are.
36D = Ivory
39D = Aqua
42D = Light Blue
Pink = 45D
Blue = 47D
Gray = 49D
Beige = 53D
 
Set of 8 wheels
 
The softer the wheel, or lower shore “D” hardness number, the more the grip and slightly less roll. The harder the wheel, or higher shore “D” number, the more the roll, with slightly less grip.  The shore “D” scale is used for rubber and plastics, while the shore “A” scale is used for urethane.
 
NOTE:   It is almost always recommended to use spacers in the wheels, when using standard 7mm bearings.  If changing from the Magnum or Giotto Wheels to the Devil Wheels, it is recommended that you lower the hardness by one Shore Level(D). For example: Magnum/Giotto 49D = Devil 47D.