BLACKHAWK! Internal Frame Kit for 603D06XX Rugged Poly blend plastic Internal frame stays -inchmoldable-inch to the Contour of your back Provides Ergonomic support and keeps the pack rigid Fits 3-day assault pack and x-1 r.A.P.T.O.R Rugged polyblend plastic Internal frame stays -Inchmoldable-Inch to the contour of your back Provides ergonomic support and keeps the pack rigid Fits 3-Day Assault Pack and X-1 R.A.P.T.O.R.