The Curv-O-Mark® Aligner Base is notched at either end for ease in aligning on the centerline of the pipe. Has two 25-pound pull, cast-in magnets for holder in either a flat horizontal or vertical position. The base will accept either leg of a standard or combination square. Will work on pipe diameters from 1" on up requiring only the extension on the legs of the square being used to accommodate larger diameters.