I would never use an Allen head cap screw, well not in a hidden location. When the next guy comes to undo the bolt he will take the hose off and wont be able to figure out why he cant get a 9/16 socket on there. after an hour or cursing he may be able to get a mirror in there with a torch to see what the heck is going on, then curse the PO for putting a Allen head Cap screw in there.