What the short description says: mount on the tailstock spindle, put a dial indicator holder in a fixed place (I use the carriage because the tailstock slips sometimes) and enjoy drilling to precise depths (say, for 3d printer nozzles ;o) ) Print using your favourite material with reasonable infill and at least 2 perimeters / 0.8mm wall thickness; the thing is designed to be rigid enough without eating a whole lot of material, and it does the job for me.