Designed to fit your AR-15 pattern firearms chambered in 5.56x45mm or 223 Remington. The clear polymer body allows you to actively monitor your ammunition. A high carbon steel spring assists the linked follower to facilitate quick and easy loading. NOT COMPATIBLE WITH SOME AR-15 / M16 / M4 RECEIVERS THAT DO NOT HAVE THE SAME INTERNAL AND EXTERNAL DIMENSION OF A MIL-SPEC LOWER RECEIVER.