I am looking at getting a few quick disconnects which just have the barb on them, no 1/4 ffl thread. I have one here already and I measured the max width and was about 7.2mm and it works fine pushing 6.7mm internal tubing on to it. The disconnect barb it about 5.6mm internally roughly. Is the barb measurement the internal diameter or external? I was just looking online and only noticed 6mm and 8mm screw on barbs for threaded disconnects. I could not find any specs for barbed only disconnects.