These KCI USA's Glock pattern magazines are constructed with a hardened steel insert that is encased in a polymer. The polymer molding helps to protect the magazine body from damage and deformation from regular use.Features :Fits: Glock 22 / 23 / 24 / 27 / 35Caliber: .40 S&WCapacity: 31 RoundsBody Material: Hardened Steel / PolymerSpring Material: Stainless Steel