The Strike Industries Modular Fixed Stock combines the versatility and adjustability of a collapsible stock with the strength, ergonomics, and solid fit of a fixed stock. The SI MFS uses a standard carbine length receiver extension and is adjusted using the included shim set to change length of pull.FeaturesCustomizable Length of Pull (12" to 14.25")Modular assemblySnap Hook attachment and sling loop For mil-spec carbine or our Advanced Receiver Extension 7-Position buffer tubes only Contents:1x Strike Modular Fixed Stock3x Adjustment Shims (0.75") Note: A standard mil-spec castle nut, buffer tube and endplate must be used for proper installation of the Viper Modular Fixed Stock