There are two gas dip tubes: KEG429 (this item) is about 1" long and KEG480 is about 2" long. They also have slightly different constructions with KEG429 having a lip at the top for the spring and KEG480 just having a rolled-over top. I'm not sure what the difference is designed for but I'm buying the extra gas tubes so I can use some silicone tube as a dip tube and I've found that the longer one (KEG480) is better for that purpose This shorter tube does work but the silicone tube sometimes gets knocked off. With the longer tube I get a whole inch of overlap on the silicone tube which makes the connection much more secure.

The tube itself is 1/4" in diameter. I don't know if something can be affixed to it but I doubt it.

The outside diameter of the tube is 5/16". As far as attaching a hose to it the dip tube is very smooth with no burr or lip. You would need to clamp it very tightly to keep it from slipping off.