These high quality plastic disconnects are a great way to protect your regulator by preventing liquid from going up your gas line.  The small additional cost will save you in the long run!

Premium Ball Lock Disconnect MFL (Grey/Gas) with Integrated Check Valve
You can now have a check valve integrated into your ball lock disconnect.

These clear/grey high quality plastic disconnects are very common in the industry but now have the added feature of having a check valve integrated into the fitting.

The internal parts are made from stainless steel and the body is clear so you can see whats inside.

With the MFL thread you can attach: 
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Recommended to be used in conjunction with .  These fittings make joining hose really easy especially if you want to use the 4mm ID Tubing.