A crescent wrench works but you may have to grind the jaws if the lugs has a taper to match. You do NOT want to try it if the jaws do n to match the sides of the lug (regardless what tools you make/use. The point that SH made about holding the barrels secure can NOT be over stated. If the barrels are NOT held extremely secure, you run the risk of breaking the solder joint between the barrels if the plug refuses to break loose and the force exerts too much torque on the joint and the barrels are allowed/able to turn. I would interested in hearing more details on the problem as it may be far better to find another way to remove whatever you have in there without removing the plugs.
