Spindle tram gage, 3/8" shank, this style of tram gage is used for perfectly aligning the spindle with the work piece. A single dial indicator is the "Old School" method that is more accurate. In the old art method a machinist will rotate the spindle 180 degrees after reading the dial then take the difference of both readings. The head tram angle is now adjusted so the indicator shows 1/2 of difference between both dial readings. This is the best method to use if you require high precision in your work.