JCT
As shown in the ZWO documentation, you remove the existing tilt plate to expose the front surface of the camera body, onto which you attach the EFW instead, using four small screws. You now have a spare tilt plate; or if you like, buy a more appropriate M54 tilt plate if you want to reduce aperture vignetting. The tilt plate then screws on to the filter wheel instead of to the camera, and becomes the flange for the combined camera/filter wheel assembly.
See blue circles in one of the images, and the description:
"The screw holes on the front and back covers shall not only allow us directly connecting the 36mm EFW to the camera and bringing the filters closer to the camera sensor, also making the it possible to match it with M68 OAG."
If you wish to use an OAG, you can attach a ZWO OAG to the filter wheel with (four) screws and then place the tilt plate on the OAG, instead of on the filter wheel. Again, the single tilt plate becomes the flange for the camera/filter wheel/OAG assembly.
Chen
