From : Wikipedia
A STANAG magazine or NATO magazine is a type of detachable firearm magazine proposed by NATO in October 1980. Shortly after NATO's acceptance of the 5.56x45mm NATO rifle cartridge, Draft Standardization Agreement (STANAG) 4179 was proposed in order to allow the military services of member nations easily to share rifle ammunition and magazines during operations, at the individual soldier level, in the interest of easing logistical concerns. The magazine proposed for standardization was originally designed for the U.S. M16 rifle. Many NATO member nations, but not all, subsequently developed or purchased rifles with the ability to accept this type of magazine. However the standard was never ratified and remains a 'Draft STANAG'
Stanag 30 Rds Magazine
The STANAG-compatible box magazine, while relatively compact compared to other types of 5.56x45mm NATO box magazines, has often been criticized for a perceived lack of durability and a tendency to malfunction unless treated with a level of care that often cannot be afforded under combat conditions. Because STANAG 4179 is only a dimensional standard, production quality from manufacturer to manufacturer is not uniform. Magazines have been manufactured with lightweight aluminum or plastic bodies and other inexpensive materials in order to keep costs down, or to meet requirements that treat the magazine more as a disposable piece of equipment than one that is supposed to stand up to repeated combat use.