Truglo fiber optic sights are high visibility, durable, and ready for service. Sights are CNC machined to tight tolerances, and fiber optic inserts Gather ambient light. Fiber optic sight technology is ideal, in that it has no half-life, as tritium only sights do, and gathers available ambient light, resulting in automatically adjusting brightness for ideal contrast. Truglo sights also glow in the complete absence of light, thanks to tritium, meaning that you can always get a good sight picture, no matter the situation.Features:- the ultimate handgun sight- uses patented technology- unbelievable transition through all light conditions- glows in the dark- no batteries required- cnc-machined steel construction- concealed fiber cannot be seen by target- fits standard holsters- snag-resistant design fits: block 42".