The AR-15 missing parts kit contains the small parts that builders need to complete an AR-15 lower receiver. It includes detents, springs, and pins for the safety selector, bolt catch, trigger guard, takedown pins, and buffer retainer. Builders use this kit to fill in any missing components from a lower parts kit. The kit fits all mil-spec AR-15 lower receivers and pairs with standard lower parts kits. It helps builders finish any AR-15 lower build without sourcing individual parts.