Now you have to attach the inner ring to the center cylinder. We have attached two pieces of geometry before so I will not go through that again here. When they are attached, extrude the poly out twice as shown.
Use the connect tool to cut a line of edges around the geometry as shown in green. Chamfer the red edges by 0.2.
Connect the arm to the inner ring by deleting the polygons at the front of the arm and then target welding the six vertices in the blue circles.
Onto the outer ring. You have to shape the outer ring in a certain way but it's a little difficult to explain so I have shown the cross-section of it in the picture. DO NOT cut the ring in half yet, I just did so in order for you to see the cross-section and be able to shape yours the same way. Once you have shaped it then you can delete half of it, but only after you have shaped it.