Rigging in the United States is typically done using a single anchor point, and pitches are rigged as a single long drop, often in excess of 100 meters. The rope is usually a thick abrasion-resistant type, which allows the rope to go over the lip of a shaft in contact with the rock. This is sometimes pejoratively called "Indestructible Rope Technique". To descend such large drops on a bobbin-type descender would be difficult owing to the thickness and stiffness of the rope, and the resulting descent would be slow and jerky. The bobbin-descender could also overheat and melt the surface of the rope. Racks are preferred as they have a much larger heat sink capacity and offer a much smoother descent on such pitches. Using the frog system to ascend long pitches is time consuming, so rope-walking systems are preferred.