This is a simple Z screw position indicator meant for the Z screws on a CR-10 (or CR-10s). I'm sure it fits others as well if they use the same size leadscrew. I have printed 4 of these and have one at the bottom and top of each screw. I level the bed, get my Z to zero, and then point the indicators directly towards the frame. If I see one out of sync from the other, then I know my gantry is likely out of level.