Used Turner Pistons for Mercury 20H or 55H engine.  All in good useable condition but all are different in ring configuration.  Pick the one you want, one groove, two grooves or three grooves. They all have the small wrist pin hole. We have not measured the diameter of these but if that matters to you we will, just ask and let us know what piston you are interested in. They all have the number 550HC cast into the inside. The price given is for one piston.