The main body of most clarinets is divided into the "upper joint", the holes and most keys of which are operated by the left hand, and the "lower joint" with holes and most keys operated by the right hand. Some clarinets have a single joint: on some basset horns and larger clarinets the two joints are held together with a screw clamp and are usually not disassembled for storage. The left thumb operates both a "tone hole" and the "register key". On some models of clarinet, such as many Albert system clarinets and increasingly some higher-end Böhm system clarinets, the register key is a 'wraparound' key, with the key on the back of the clarinet and the pad on the front. Advocates of the wraparound register key say it improves sound, and it is harder for moisture to accumulate in the tube beneath the pad. Nevertheless, there is a consensus among repair techs that this type of register key is harder to keep in adjustment, i.e., it is hard to have enough spring pressure to close the hole securely.