This is the one piece main bearing block with swivel servo mount. This offers several advantages, as demonstrated in the video, such as the ability to remove left and right servos as a unit for motor adjustments or servo arm replacement as well as the benefit of a fully enclosed main shaft within the frame. It does require some re-thinking with regard to the rear servo installation because the rear servo mounting location is sunk into the assembly. I believe the idea is to bring it in closer to the COG, but it sorta makes it a pain to properly install the rear servo. I had to flip the ball and use a ball without a standoff to get it the way I liked it.