Streamlight TLR, which is one of more popular weapon lights, comes with 4 rail notch inserts, all of different widths: Glock, Beretta 92, 1913 (Picatinny) and TSW/99.
What are the railed handgun manufacturers thinking? Not 2, not 3, but 4 different slot widths instead of 1 standard 1913 which is only a tad wider.