This adapter makes it quick and easy to switch your Regulator between a Grey MFL Disconnect and a hose line when using a full size CO2 tank.
You could use a 1/8" NPT to 1/4" Barb to go directly into the regulator but then you need to re-apply Teflon tape every time you switch back to portable mode using the Grey MFL Disconnect and 16g Cartridges.
The technical term for the 1/4 MFL thread is 7/16-20UNF male
Pro Tip:
This adapter is perfect to attach to a dip tube to weigh it down when using the keg on its side.