Park Tool BBT-7 Bottom Bracket Cartridge Tool (XTR) The BBT-7 Lockring Wrench is used for installing and removing the lockring used on Dura Ace 7700 and XTR 950 Bottom Brackets. It is laser cut and engages five of the lockring's six notches for a precise, secure fit. The handle is vinyl dipped for comfort. While made specifically to fit Dura Ace and XTR Lockrings, it also fits several other lockrings as well.