The term Mil-Spec is a colloquialism that describes items built to certain dimensions, materials, and tolerances specified by the U.S. Military. In some cases, it is important to know if your firearm is built to military specification—particularly when adding accessories or modifying the platform. Many firearms enthusiasts prefer guns that are built beyond Mil-Spec for additional function. For example, a Mil-Spec trigger on an AR-15 is perfectly functional, but many AR owners want a trigger with a more ergonomic shape, lighter weight, and better material design.