Tubing sleeves made of plastic or metal are used in many areas of pneumatics because, with all their advantages and disadvantages, they are among the simplest and most robust of tube connectors. Generally, one end is simply pushed into the tube. A cap nut or adhesive fitting, for example, is placed over the other end. In comparison with other systems, such as threaded constructions, sleeves get good marks for their larger hose diameter, extremely simple assembly and disassembly, compactness, aesthetics, and the fact that no additional securing element is needed. There is a slight trade-off, particularly in versions without securing elements, in sealing. Screw connections can compensate for somewhat higher system operating pressures. This disadvantage of sleeves can be negated to an extent with rings, which can be flexibly added as needed at some slight expense to aesthetics.