This is the 20 round HK416 and MR556-A1 magazine from Heckler & Koch. in 5.56x45mm / .223.
Manufactured in Germany this all steel design is the most recent 'maritime' version which has a higher grade black finish than previous versions. All parts including the follower being fully coated.
This HK stamped magazine is compatible with all AR15 and STANAG format rifles. This magazine is new from factory and offers extreme durability with an excellent finish.