This is the XS Scuba PonyPac Harness Pony Cylinder Backpack Features: Comfortable harness designed to carry a pony cylinder on your back Fits 13, 19, 30, 40 cu ft pony cylinders with 4.0" - 5.4" diameters Two trim weight pockets with Velcro release carry up to 5 lbs. each Includes two short length tank cam straps (p/n BP550) Two stainless steel D-rings Neoprene neck collar Two-way adjustable sternum strap Great device for the boat, beach dives, swimming pool maintenance, or ocean kayaking, the XS Scuba&';s PonyPac Harness is one versatile harness. "