CCR divers use Swagelok QC6 connectors to plumb in offboard gas. The QC6 has sufficient flow for breathing gas, which is essential whenever a BOV is being used. We use genuine Swagelok 316 stainless with double shutoff service.
The male QC6 is rethreaded to 9/16″-18 male (no adapters) to connect to the 2nd stage end of a LP hose. This makes the male QC6 as short as possible.