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

MAGNUM 49D, 53D, 57D, and 60D – 63mm  Standard Loop Figure Wheels 

Hardness:  Gray 49D, Cream 53D, Yellow 57D, and White 60D
Diameter:  63mm
Compound:   MonoCompound Elastomeric ThermoPlastiche Formula

The Roll-Line 63mm Mangnum Wheels have a medium profile that makes Magnum 63mm the ideal choice for the execution of loops and the optimal diameter for the maximization of roll. The Magnum 63mm are available in four colors/hardnesses.