Estone New Internal Single Purpose HI-LO Welding Gage Gauge Root Gap mm Unlock the retaining screw. press the gauge legs beyond the barrel Insert the legs (wired) into the root gap space or the two pieces of pipe to be fitted Hold the gauge as square as possible with the fitting to obtain an accurate reading. When the red line aligns with the 1/32 increment line you have a good internal alignment and fit-up.