Manifolds allow you to have one CO2 tank with multiple lines. Each line can be turned off individually without affecting flow to other kegs. Each ball valve contains a check valve that ensures no beer or gas can flow between the two kegs. The barbs are all 5/16", standard for gas line in the beer industry.
NOTE: The barbs are 1/4", for gas line on standard homebrew kegs, so this is NOT the Manifold you want for homebrew / soda kegs