This is the 12 STD version of the Incube. 12 STD refers to the axle size that the wheel uses, and is larger than the industry standard. Please check to see if your fork and deck are compatible with these wheels. The Incubes uses a 7 spoke core design, and a 88a urethane durometer. This durometer is ideal for all styles of riding, and terrain; offering a good balance between grip, and speed. These wheels are sold individually, and do come with preinstalled bearings.