ETS magazines are made from advanced polymers that provide extreme impact resistance so they won t crack or break when dropped. With superior heat cold and UV resistance these magazines wont become brittle over time even when exposed to harsh environments chemicals or extreme cold. Its durable construction eliminates creep so the feed lips and body wont spread when being stored long term even when fully loaded. ETS magazines for Glock pistols feature a translucent body allowing you to see your ammo count.This model has a 12round 40 SW capacity and is compatible with Glock 42.