Used for creating a reference line on 1/2 PVC pipe. Helpful went drilling several holes in pipe for 12mm pixels. Reference line insures that your drilled holes don't start to spiral.

Simply clamp the 1/2 PVC pipe to a workbench or board. Place a sharpie in the holder and slide the holder/sharpie down the edge of the pipe creating a reference line.

As you drill your holes make sure the drill bit stays on the reference line.