A backplate is a component of a buoyancy compensator used in scuba diving to support diving cylinders on the diver's back. Heavy-duty, metal backplates are mainly used in technical diving where the diver typically carries two main cylinders on the back and two stage cylinders slung on each side of the body throughout the dive.
A backplate is generally constructed of stainless steel or aluminium, although there are variations made from plastic ABS, titanium and brass. The backplate has a raised ridge running down the centre, and one or more pairs of holes with 11 inch / 27.5 cm centre-to-centre spacing between the holes. These holes are used to mount either a set of doubled scuba tanks / twin diving cylinders, or an adapter for diving with a single tank. Backplates are generally paired with a wing - an enclosed air cell that allows the diver to add or remove gas to control buoyancy. A harness, with shoulder straps, a waist strap and possibly a crotch strap, is threaded through the backplate to link the backplate to the diver's back.
Backplate designs differ from manufacturer to manufacturer, however some incorporate slots for tank camstraps, as some wings allow camstraps to be threaded through them to hold the tank.
This configuration is often called a Hogarthian rig, and is a core component of the DIR diving equipment configuration.
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