SP System - M4 Series HPA Adapter and Magazine for Tokyo Marui MWS GBB System.
 
Features
Durable and precise CNC 6061 aluminum construction
Allows Tokyo Marui MWS rifles to use HPA and AEG magazines
Compatible with mid-cap and high-cap AEG M4 magazines
Feed windows allows accurate and easy alignment with magazines
Comes with an EU and US input adapter