Because the subjects of model robot kits are typically humanoid and/or possess limbs, joints are required in order to make the finished model poseable. For decades, poly-caps were and still are used for this purpose, although they tend to degrade over time and thus have been less frequently used since the 2010s. Hard plastic joints generally exhibit greater friction than polyvinyl joints, and are similarly more durable than polystyrene joints. ABS joints, however, require greater precision in tooling to ensure easy assembly, and in some cases, they require screws and a small gap between parts.