This bracket is designed to hold a MaxBotics LV-MaxSonar-EZ type sensor, popular with hobbyist robotics. The LV-MaxSonar-EZ sensors have a sensor body of 16.4mm in diameter, with mounting holes offset 8.5mm (up and down), and 6.6mm to each side. "Up" means the bracket is oriented so that the double mounting tab is on the bottom. The photo shows a EZ4 (1040) sensor attached. Print these out, and use nylon screws to fasten the parts together. It's OK if the sensor PCB doesn't sit flush on the back of the bracket, it will be secure. Mount the bottom bracket to the mounting surface with velcro dots for easy adjustment. Download the .STL file, slice it with your favorite slicer, and print it. Currently, Slic3r reports one non-manifold location associated with the mounting tabs and the vertical geometry around there. I have tried to eliminate this, but cannot. The geometry slices OK, and prints fine. Once this is resolved I will update the STL file.