Truglo uses fiber-optic technology to pick up visible and UV light. They are bright in low light conditions such as dusk and dawn but work very well in full daylight. This pair has contrasting red front and green rear sights to help align them easily. A smooth, snag free design so it will not catch on clothing and fits in most standard holsters. This particular set was made in the USA, it fits the Glock 20, 21, 25, 28, 29, 30, 31, 32, 37, 40, 41. It is recommended for the Gen 4 Glock. Solid CNC steel and treated with a "fortress finish".