The BTU adapter kit contains the BTA adapter plate and the BTSS3007 locking component designed to work with the BT1 coupler lock.  This kit allows the BT1 to cover all applications of the BT1, BT2, BT3, and BT4 coupler locks.  By adding and/or interchanging these components into the BT1 coupler lock you have the most versitle coupler lock on the market.