A pillow block specifically for use with Thomson Super8 ball bushings (fits 1/2" round guide rails). The bearings have floating races to compensate for misalignment. A single 6-32 screw allows the "fitment" of the bearing to be adjusted. This part mounts using 4x 6-32 screws spaced in a 25mm square pattern. The flat surface is 19mm (about 3/4") from the axis of the guide rail. The mounting holes are 13mm deep. Sorry for the mixed units. I live in a backward country... Print with 0.2mm layers and 30% infill. No support material is necessary. Cura sliced it well, Slic3r had problems.