Attaches to the Compound Tube or Corner Finishing Box and applies the correct amount of joint compound as the pre-fill coat to internal corner joints and applied coats after the Corner Roller process. Built TradeTuff® handmade with Delrin roller wheels, USA billet aluminium and steel components. The 2-wheel design leaves less compound for better control. 4-wheel design provides more compound for a smoother run. 5-year warranty.