Each hole contains a specially formed nut to allow shaped grips to be screwed on the wall. The front of the board is covered with fine sand glued to the surface to provide additional friction. In addition to the grips, the wall may contain additional surface structures such as small indentions and protrusions, or take the form of an overhang.
Some grips are specially formed to mimic the conditions of outdoor rock, including some that are oversized and can have other grips bolted onto them. Grips come in different colours, those of the same colour often being used to denote a route, allowing routes of different difficulty levels to be overlaid on one another. The grade of the route is usually a consensus decision between the builder of the route and the first few people who climb the route.