M2 bowden drive

This is the bowden drive for my dual e3d hotend design found here.
http://www.thingiverse.com/thing:824403

There are 2 versions of the part. The 1b1 version is still designed for the tube holders that came with my e3d hot ends bowden kit. They are pass through 10 mm thread types. Which means that the tubing can go all the way through the holder. I put stops in the passage that will prevent the tubing from being sucked back into the extruder gear when it retracts during printing. The larger