Steel Cylinders have round bottoms and need to have a cylinder boot. XS Scuba's Cylinder Boots are manufactured using high quality injection-molded construction with a self-draining and durable design. The boot is equipped with an octagon rim to prevent the cylinder from rolling while it is lying down. Boot protects the cylinder bottom from damage and allows the diver to stand the cylinder up right to aid in regulator and BCD mounting. Boot is designed for cylinders with an 8.0" (20.3 cm) diameter.