Hand selected to ensure a proper fit between upper and lower halves. This "better than mil-spec" set accepts all aftermarket and mil-spec internal parts."Multi" caliber marked. Not "T" Marked for a custom look. GI style Upper and Lower machined from 7075-T6 Aluminum USA-sourced forgings. M4-style feedramps for flawless feeding. Will accept all mil-spec parts. Multi caliber Markings Black Armor-Tuff finishDue to the nature of forged lowers, some pitting and machine marks are natural and unavoidable. Please do not be alarmed by these marks, they do not effect function.