Depends on when it was made. Very early models from chantilly or sterling only used 2 (one wavy, one flat). After that point they all used 4 (flat, wavy, flat, retainer). Now if you have a sure-fire or other worn out forend light that was purchased from a used police auction, please keep in mind that most of these can be broken and depending on how worn out it is depends on how many washers they may have used to tighten it up. Personally I dont like them. They're heavy, break easily and hardly ever fit right. I'd rather use a hand held light. When the "real scenario" happens trust me, using that light will be the last thing on your mind. I've never been in a situation when it would have come in handy.