This is a two piece mount to help support an adjustable shelf for a projector. The back of the shelf will be hinged to the wall, and the front will have two of these assembles.
The two pieces slide together over a 1/4" turnbuckle eye. I am using a 1/4" threaded rod with a turnbuckle at the shelf end and a rod end clevis and pin eye bolt at the ceiling. Note that one end of the turnbuckle is right hand threads and the other end is left hand threads. You can replace the right hand side with standard threaded rod, but not the left hand side. So I am using this mount on the left hand side of the turnbuckle.
I could not find a mount like this so I designed and printed one. I printed it with 4 shell layers and 40% infill, it is very strong, I could not break it with my hands. I probably could have printed the clevis' but I ordered them instead. The turnbuckles were only $1.13 at Menards but are plenty strong for this application. The bolt holes are 4 mm and work with #6 bolts. The main pivot cylinder is 9 mm diameter.
A side note about projectors. I made this to support a projector and expected to adjust the angle of the shelf about 10 degrees down, so the projector would be aiming directly at the screen. Wrong! Doing so made it necessary to use the keystone adjustment, which does make the picture rectangular again (as opposed to a trapezoid) but it ruins the aspect ratio, so the picture will not fill the screen (you have empty spaces either top and bottom, or on the sides). The correct way to do it is, mount the projector level so it is 90 degrees and square to the screen. Then use the lens shift adjustments, and do not use any keystone adjustment at all. This way you can keep the correct aspect ratio (16:9 in my case).