This is the Yukon Dana 44 Steel Spool replacement. (Part number YP FSD44-3-30DN) Yukon performance spools are made from the highest quality materials to ensure high strength and long life in performance applications. Yukon Full Spools are a cost-effective way to convert a diff to 100% lockup. Installation is easy as they install in place of your differential carrier assembly. Each Yukon spool is made from high-quality 8620 steel and heat treated for additional strength. A spool is an outstanding choice for dedicated off-road and drag racing vehicles only.