This is a set of NPR 10-911 Pistons (STi for D25, V25, or W25 Heads) that have been machined for clearance for the H Beam Rods to fit.   The webbing of the piston from the tapered wrist pin design is very tight, so we machine clearance (.080") on the inside of the piston.   There is not a lot of material to take off.  The pistons are more out of balance brand new, than when we put them back in the box, as we weight match the piston sets.  The manufacture has these pistons 2.0 grams out of balance; or "balanced within 2 grams".   We do better with these modified pistons as we know the will be used in performance applications.