Sig Sauer Grip Module Assembly, Fits Sig P365 Fire Control Units Except Manual Safety Variants, Includes Small, Medium, and Large Backstraps, Black 8901179 Factory replacement for the P365-XMACRO grip module. It features a true 1913 accessory rail and three interchangeable backstraps (S" M" L) to ensure a proper fit for the user's hand. The medium backstrap comes preinstalled.