A dial Indicator is a great way to fine tune your printers bed. This mount is a quick and convenient solution to quickly secure your dial indicator to the extruder for bed leveling. All that is needed are two 3mm x 10mm screws to secure it to the extruder, and your ready to go! The The mounting hole is 10mm in diameter. I use a Fowler FOW72-520-110 Dial Indicator and it fits very securely.