AR-STONER Magazine Rebuild Kits keep your 30 round AR-15 (223 Remington, 5.56x45mm, 300 AAC Blackout) magazines in tip-top shape. This kit is handy when your old mag springs are worn and need replacing or if the follower in your magazine no longer activates the bolt catch. Designed to replace the internal parts of an aluminum USGI magazine, these springs and followers are useful to keep your pre-ban, normal capacity AR-15 magazines operating at their full potential. Features3 - 30 Round Chrome Silicon Springs3 - Followers (AR-15 223 Remington, 5.56x45mm, 300 AAC Blackout)3 - Base plates