Hand selected to ensure a proper fit between upper and lower halves. This Wilson Combat ATR-15 matching receiver "better than mil-spec" set accepts all aftermarket and mil-spec internal parts. "Multi" caliber marked. Not "T" Marked for a custom look.FeaturesGI 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 (forging stamp may vary)Anodized Black finish