this is a 12mm support block with two tiedown openings on the shaft clamp, the holes are designed for a M3 bolt and Nut, both sides are countersunk. the part is 15mm wide so fits perfect on OpenBeam extrusion as i have designed this for a 3d printer im building using Open Beam, i will be uploading a lot of parts shortly now that i know i can design and print with good quality. In reality this fits anything that can be mounted to with M3 bolts, the surface mounts are all M3 holes Countersunk. Let me know what you guys think, as far as my experience is its very rigid Spec/Dimensions: Total Length = 50 mm Total Height = 45 mm Total Width = 15mm Supports 12mm Smooth Rods Support Hole openings for M3 Nut and Bolt All Mounting holes are Countersunk