Q. "There are letters and/or numbers after the model number inside my Kohler toilet tank - what do those mean?"
A. Kohler offers many variations of almost all their toilet models, and has experimented in the past with many different features. Typically, numbers (or a single letter/number combination like K4 or Y2) after the 4- or 5-digit model number indicate the color code for your toilet. If your model number is followed by letters, those usually have different meanings to indicate the features of your toilet or will indicate that you have a specialty Artist Edition toilet.