I looked through all the DMC and Volvo literature and can't find it. You could probably measure the diameter threads & use a machinists reference.
I tighten them to "snug". It's an O ring seal and not dependent on torque to prevent vacuum leak, plus its a fine thread so a little goes a long way.
I just tighten until the tube won't rotate then just a touch more. Once the hoses are connected that will act to lock the tube in place.