The Assault RC 5mm to 4mm Gold Plated High Current Connectors will fit any 4mm or 5mm battery insert with one plug. The highly conductive gold plate coating insures high current from the battery to pass through and give you as much from your battery as possible. It has a low profile head for a perfect solder joint to fit any application. These plugs are also a great way to build charge leads and not have to have more than one for each size bullet when charging different packs. A must have for all serious electric rc racers.