This is a digital indicator mount for the Prusa Mendel i2. This mount is designed to slip in between the X-axis smooth rods and have the standard LM8UU bearings slide into the mount. The mount hole for the digital indicator was designed to fit a 9.5mm collar and I've added a link below to the indicator I have purchased. I apologize in advanced for the print quality of the part as I'm currently re-calibrating the machine and I printed the part at 400 Microns to speed up the print time Digital Indicator: http://www.harborfreight.com/1-inch-sae-metric-digital-indicator-93295.html.