Metric magazines have a small front locking lug (1/4 inch wide) that is merely punched out of the body of the magazine. Metric magazines also have a slim floorplate that is NOT wider than the body of the magazine. In contrast, inch pattern (British Commonwealth) magazines have a relatively large and beefy (1/2 inch wide) front locking lug that is welded onto the front of the magazine. They can also be distinguished by their floorplates, which are wider than the magazine body and have a "button" release on the bottom.
