AmeriGlo Rear Only-Green Tritium Lamp 2-dot White Outlines .165" Sq Notch. The square notch allows for quick acquisition of the front sight which in effect gives you a "mini-dot" which is a more precise horizontal sight...which is the whole point of a pistol after all. The well-defined notch with the sharp corner allows quick acquisition of the rear sight which in effect gives you a better view of your target letting you shoot more accurately. Since the tritium is aligned on an hourglass shape the notch doesn't have to be filled or gaps put you out of the sight picture. Specifications for AmeriGlo SW/M&P Tritium Rear Sights: Manufacturer: AmeriGlo Color: Black Rear Sight Color: Green Tritium Sight Style: Square-Notch Package Contents: AmeriGlo SW/M&P Tritium Rear Sights AmeriGlo SW-470R: Rear Only-Green Tritium Lamp 2-dot White Outlines .165" Sq Notch