This is the Highland STA Single Tank Adapter

Features:

• 14 gauge (.074/1.9 mm) 316 grade stainless steel
• A quick, easy way to mount a single cylinder to a backplate and harness
• Attaches to cylinder with two cam bands
• Center-to-center distance of 11"
• Includes hardware
• Weight: 1 Pound

For divers who frequently switch between double tank and single tank rigs, Highland by XS Scuba's Single Tank Adapter is a convenient way to attach cam straps to a hard metal back plate that does not have tank band slots."