water capacity, as that is how it is measured and marked (WC) on the cylinder (10 liter, 12 liter, etc.). Cylinder working pressure will vary according to the standard of manufacture, generally ranging from up to . An aluminium cylinder is thicker and bulkier than a steel cylinder of the same capacity and working pressure, as suitable aluminium alloys have lower tensile strength than steel, and is more buoyant although actually heavier out of the water, which means the diver would need to carry more ballast weight. Steel is also more often used for high pressure cylinders, which carry more air for the same internal volume. The common method of blending nitrox by partial pressure requires that the cylinder is in "oxygen service", which means that the cylinder and cylinder valve have had any non-oxygen-compatible components replaced and any contamination by combustible materials removed by cleaning. Diving cylinders are sometimes colloquially called "tanks", "bottles" or "flasks", although the proper technical term for them is "cylinder" or "scuba tank". Harness configuration The scuba set can be carried by the diver in several ways. The two most common basic mounting configurations are back-mount and side-mount, and back-mount may be expanded to include auxiliary side-mounting, including bungee-constrained low profile side-mount, and the less compact sling-mount or stage-mount arrangement. Most common for recreational diving is the stabilizer jacket harness, in which a single cylinder, or occasionally twins, is strapped to the jacket style buoyancy compensator which is used as the harness. Some jacket style harnesses allow a bailout or decompression cylinder to be sling mounted from D-rings on the harness. A bailout cylinder can also be strapped to the side of the main back-mounted cylinder. Another popular configuration is the backplate and wing arrangement, which uses a back inflation buoyancy compensator bladder sandwiched between a rigid backplate and the main gas cylinder or cylinders. This arrangement is particularly popular with twin or double cylinder sets, and can be used to carry larger sets of three or four cylinders and most rebreathers. Additional cylinders for decompression can be sling mounted at the diver's sides. It is also possible to use a plain backpack harness to support the set, either with a horse-collar buoyancy compensator, or without any buoyancy compensator. This was the standard arrangement before the introduction of the buoyancy compensator, and is still used by some recreational and professional divers when it suits the