I am always tinkering around and trying to design cheap alternatives to store bought or specialty parts. While CNC couplers are not all that expensive (if ordered from China...) I wanted to build a cheaper one.
By using off the shelf hardware store stuff a simple coupler could be built that I think works a little better than the gas line and hose clamp option.
The cost to make these couplers is only a few bucks if you have an old tap and die kit around. Even if you need to buy the tap kit it's still pretty inexpensive. (And having a tap kit around is always useful.