This is a brass weight designed to be fastened to the left-front corner of the chassis, first seen on the 4.8, just in front of the battery where your receiver mounts. At just .050" thick and coming in at 0.5oz, this is a great way to place more weight in front of the battery while being as low-profile as possible. Conveniently fastens to the chassis using (2) 4-40 button head screws; no tape!