Sig Sauer P320 Striker Captive Housing is constructed of steel and featuring a durable nickel finish. The housing is designed for the P320 pistol model from Sig chambered in either 9mm, .357 SIG, .40 S&W or .45 ACP. Housing the striker, striker spring and spring cups, the captive housing retains and secures crucial firing components inside the firearm. This OEM part is perfect to replace you original worn parts, or to just keep your Sig Sauer firearm running in top operating condition.