a particular diver, but are more often adjustable. Sometimes a quick release buckle is added to one or both of the shoulder straps. The waist belt has a buckle for closing and release. and the waist belt is usually adjustable for security and comfort. Various attachments have been used to attach the harness straps to the cylinder bands. A crotch strap is optional, and usually runs from the lower cylinder band to the front of the waistband. This strap prevents the set from riding upwards on the diver when in use. This arrangement is still occasionally seen in use. Backplate or backpack harness The characteristic difference between this and the basic harness, is that a rigid or flexible backplate is added between the cylinder and the harness straps. The cylinder is attached to the backplate by metal or webbing straps, and the harness straps are attached to the backplate. In other respects the system is similar to the basic harness. Methods of fixing the cylinder include metal clamping bands, secured by bolts or lever operated clamps, or webbing straps, usually secured by cam buckles. This style of harness was originally used in this simple form, but is currently more usually used with a back inflation wing type buoyancy compensator sandwiched between the cylinder and the backplate. Cam bands The combination of webbing strap and cam action buckle that is used to secure the cylinder to a buoyancy compensator or backplate is known as a cam band or cam strap. They are a type of tank band, which includes the stainless steel straps used to hold twin cylinder sets together. They generally rely on an over-centre lever action to provide tensioning and locking, which may be modified by length adjustment slots and secondary security fastening such as velcro to hold the free end in place. Most cam buckles for scuba are injection moulded plastic, but some are stainless steel. Many recreational scuba harnesses rely on a single cam band to hold the cylinder to the backplate. Other models provide two cam bands for security. A cam band can also be used on a sling or sidemount scuba set to attach the lower clip to the cylinder. Tank bands Stainless steel tank bands are the standard method for supporting manifolded twin cylinders, as they provide good support for the cylinders, minimise loads on the manifolds and provide simple and reliable attachment points