Primary, Tapp to expensive. Made my own Hi-Capa M4 Adapter and its even better! : r/Speedsoft
Airsoftjunkiez: Monk Customs M-Adapter For TM Hi-Capa | Popular Airsoft: Welcome To The Airsoft World
I know a lot of people hate the Primary Airsoft adapters, but when it's 110° outside, a light kit is a life saver. Also a great first step into HPA : r/airsoft