If you are making your own cables, go to a good welding supply store. Take a plug with you. The Nato plugs have large fittings. They also should be water proof. Each side of the plug needs proper fitting little "O" rings in the fittings. Also, the military grade cable has a jacket more than twice the thickness than the cable commonly found on welding cable so be careful, the welding cable is easliy nicked. The best fitting welding cable in the Nato plug is the 1/0. Larger welding cable does not fit the plug well, if at all. If you must use welding cable on the Nato plug, shorter is better but can be less than practical on occasion. The best bet is to be patient and purchase a proper mil-spec cable. One without caps and sometimes even a missing back is good. They should be cheaper. Just make sure the actual cable is free of nicks and other flaws. You can buy new replacement Nato plugs rather easily.