Real Avid AR15 Vise Block - The revolutionary design of the Smart Fit Vise Block adjusts to fit every AR15 magazine well out there. The Smart Fit allows you to work on your lower receiver with a solid foundation for changing out buffer tubes or fixed stock receiver extensions. Insert the block into the magazine well and simply rotate the adjustment handle to tighten the fit. Fits .223/5.56 AR15'sOversized edge for precise fitKnurled texture for improved gripMagazine lockExpanding sections custom fit any magwellPivot LockThreaded post adjusts wedgeAdjustment handle