Bastion rear slide back plate is a custom, high-quality pistol accessory for FULL-SIZE Sig Sauer P320. Compatibility: P320 9mm, 357 SIG, 40 Cal. NOT COMPATIBLE with P320 45 AUTO; P320X; M17, M18 or LEGION series. Replaces plastic factory part for strength and durability Personalizes / identifies firearm T6-machined aluminum Hard-coat anodized black Laser engraved design won't rub off