It fits the Marshall 651STX monitor, and could probably fit several others with modifications. For mounting tto your sled, it has a 1/4"x20 thread in the middle, 2 10-32 holes at 1" center to center around that, and 2 1/4" holes that allow the yoke to screw directly on to the end of Cinetronic monitor rods.
I sold these for $250 when I was making a little business of selling these. Since this one is well-used, and shows wear, I'm asking $175 for it, plus shipping.
Check out the pictures and shoot me an email if you want this. Email or call - email@example.com or 215-796-8938. The last used one of these I sold went in hours.