Clearance for piston to wall clearance is made at the shirt not the top ring. Ring end gap is based on bore diameter as well. Forged pistons are clearanced at .004 to 5 thousands. The measurement of .0015 is 1 1/2 thousands. .005 has been the sweet spot for forged pistons. The piston materials used today are of much better quality and grow less than materials used in yester year.
