The Pony Pac is a quick, easy way to hit the water. This makes it attractive to first responders, maintenance divers, aquarists or anyone who doesn't require an air bladder on their harness. Comfortable, streamlined way to carry a pony cylinder on your back Fits 13, 19, 30 or 40 cu. ft. pony cylinders with 4.0 - 5.4" diameters Two trim pockets, with hook and loop release tabs, hold up to 5 lbs. (2.3 kg) each Two stainless steel D-rings for critical accessories Rolled neoprene neck collar for maximum comfort Knife mounting grommets are ideal for Rook Knife (p/n KN500) Two-way adjustable sternum strap Includes two short length tank cam straps (p/n BP550) Extra large thumb loops for cinching down shoulder straps Available in three sizes Small 25" - 35" waist (p/n BC503) Regular 30" - 50" wasit (p/n BC507) X-Large 45" - 55" waist (p/n BC509)