My son ordered 4 pistons for a Pontiac OHC 4 from Rock Auto, and recived 3 of one design, and 1 of another, althoe all four were correct size, ect. Rock Auto saw no problem with that and could not understand why my son would. It took FOREVER (many e-mails, long distance phone calls, pictures, ect.) to get an exchange of 4 alike pistons. And Rock Auto was not happy about it at all. Added 4 or 5 weeks to his rebuild.