Accessory to attach US Legends-sized Groove on the back of Rook to make the combined mode achieve a closer look to G1 Defensor. When not in use, it can peg on the 5mm post on the side of Groove.
You can only use this when Rook is mistransformed in leg mode - which requiers the other leg - either Streetwise or First Aid - to be raised by either stacking two CW feet together, or using my adaptor.