This is the instrument part of the TiltAdjuster. It connects with the extension tube adapter with threads. You have to purchase the adapter that fits your extension tube in addition.
 
For Generation 2, the TiltAdjuster has been redesigned as two separate components: the instrument and the adapter. This decision was made to improve the quality and precision of the adapter’s interface surface. Although the original concept was to permanently bond the two parts, testing showed that the threaded connection provides sufficient rigidity without the need for adhesive. The Generation 2 TiltAdjuster is therefore assembled by screwing the instrument onto the adapter.
 
When using a Generation 2 TiltAdjuster, the USB cable should be secured to the adapter to prevent any mechanical load on the instrument during adjustment. Rotation of the TiltAdjuster must always be performed by holding the adapter, not the instrument itself.