You don't have time to fool with unreliable tools. That's why the Curv O Mark Centering Head Pipe Marker (Standard) is a must-have on your list of pipe welding tools;This pipe centering tool helps with setting center lines, establishing angles and marks for butt-ins, locating points inside pipes and tanks, laying out keyways and measuring declivity;Standard #6 Model may be used on pipe 1/2 in diameter and larger; use it for pipes and tanks;The CurvOMark center finder has a 4 inch Y-type head fitted with an adjustable dial bubble protractor (DSL);Use this manually operated Jackson Safety hardened centering pin with a small hammer or mallet to tap the pin in for effective pipe marking