hi all names andy i own a cherokee thats had the beam fitted but i also work for a main jeep dealer in uk so have first hand experience of this situation lol the tool is in 3 parts one is for the grand cherokee and the othjer is for the kj the smaller end of the spoon ( as its known) is 23.5 mm in diameter and is used to measure the clearance in the centre if a tank guard is fitted the other curved spoon is used to measure the clearance at each end of the bar, not the side but the end. if you get my meaning. We have been moving fuel tanks forward and have had some good results, the THULE/BRINK/MOPAR bars have been passing with no issues after sliding the tank forward. Whoever siad it is not allowed to move the tank is talking bull as i have reported this directly to jeep technical who have now been advising the factory and FCA direct. They ARE working on a fix and have been for some weeks but wont release any details till all testing has been done. hope this helps
cheers andy
