The hardness (or durometer) determines the grip and slip of a wheel. Durometer is measured either on the A or D shore scales, where a higher number is a harder and more slippery wheel. Skaters may choose wheels based on their skating discipline and the floor type they are skating on (wood, sport court, concrete, etc.). Normally, a harder wheel with more slip is used for turn figures. Figure skaters often elect to use a mix of wheel hardnesses on their skates to optimize turning and acceleration, with a softer "push" wheel. Freestyle skaters tend to use a mix of hardnesses on skates, using a harder wheel on the edge they need to spin and a softer wheel on the other edges. A typical freestyle wheel will range from 92A–103A or 35D–61D. A softer wheel with more grip is used for dance. Popular quad wheel brands include Roll-line, Rollerbones, Komplex, and Boiani.