The Luth-AR Modular Buttstock Assembly (MBA) for AR style carbines is designed to replace the standard buttstock on your AR. The MBA-4 is designed to work with a 6-position Mil-Spec or Commercial buffer tube. The MBA-4 is a direct replacement a standard adjustable carbine buttstock without additional Length-of-Pull or Cheek rise in a low-cost, lightweight, strong and high-quality design.