Nighttime and low light shooting tests prove sights equipped with these glowing dots are easier to see and more accurate than instinctive shooting with standard black sights. Rugged, heavy duty, Traser, luminous, 3-Dot tritium lamps provide their own long-lasting energy source. Lamps are mounted in silicone-sealed, metal cylinders to give maximum protection from breakage or leakage. Polished sapphire, crystal windows give a bright, crisp and perfectly round aiming dot in low light. Inlaid white rings around each sapphire make the sights appear as standard white dots in daylight. Very narrow blades do not have the white ring and will look more like a plain black blade in daylight. Mos Mfg: Trijicon SPECS: Steel, blued with tritium inserts. Sights listed as Fxd. fit guns originally equipped with factory, fixed sights. S&W models fit 3rd generation only, will NOT fit guns originally equipped with plastic sights.