itchy skin rashes. Over time, this can lead to breakdown of the skin. On the other hand, a very tight fit may excessively increase the interface pressures that may also lead to skin breakdown after prolonged use. Artificial limbs are typically manufactured using the following steps: Measurement of the residual limb Measurement of the body to determine the size required for the artificial limb Fitting of a silicone liner Creation of a model of the liner worn over the residual limb Formation of thermoplastic sheet around the model – This is then used to test the fit of the prosthetic Formation of permanent socket Formation of plastic parts of the artificial limb – Different methods are used, including vacuum forming and injection molding Creation of metal parts of the artificial limb using die casting Assembly of entire limb Body-powered arms Current technology allows body-powered arms to weigh around one-half to one-third of what a myoelectric arm does. Sockets Current body-powered arms contain sockets that are built from hard epoxy or carbon fiber. These sockets or "interfaces" can be made more comfortable by lining them with a softer, compressible foam material that provides padding for the bone prominences. A self-suspending or supra-condylar socket design is useful for those with short to mid-range below elbow absence. Longer limbs may require the use of a locking roll-on type inner liner or more complex harnessing to help augment suspension. Wrists Wrist units are either screw-on connectors featuring the UNF 1/2-20 thread (USA) or quick-release connector, of which there are different models. Voluntary opening and voluntary closing Two types of body-powered systems exist, voluntary opening "pull to open" and voluntary closing "pull to close". Virtually all "split hook" prostheses operate with a voluntary opening type system. More modern "prehensors" called GRIPS utilize voluntary closing systems. The differences are significant. Users of voluntary opening systems rely on elastic bands or springs for gripping force, while users of voluntary closing systems rely on their own body power and energy to create gripping force. Voluntary closing users can generate prehension forces equivalent to the normal hand, up to or exceeding one hundred pounds. Voluntary closing GRIPS require constant tension to grip, like a human hand, and in that property, they do come closer to matching human hand performance. Voluntary opening split hook users are limited to forces their rubber or springs can generate which usually is below 20