The EZ-ON Pony Mount is designed to attach a small 'pony' cylinder to your primary dive cylinder. The pony mount is made of coated aluminum, the quick-release buckle is constructed from 316 grade stainless steel and the strap is { 1 in | 2.5 cm } adjustable length nylon webbing with a velcro tab. This is designed for 4.4" diameter cylinders - aluminum 8, 13 and 19 cu ft. The mount is held secure underneath the { 2 in | 5.1 cm } tank strap of the primary cylinder, and the quick release buckle provides easy removal of the pony cylinder. Rubber feet on the mount protect the cylinders from scratching. If wish to use the pony mount with doubles, you will need to add a standard Cam Buckle Tank Strap around one of the cylinders in the doubles set in order to use the pony mount.