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. Non-pressure tested, it is advised to preform a leak test prior to hooking up gas line to insure no leaks.