The Alloy USA H/D ball joints have been designed with a low profile (grease) zerk fitting for regular maintenance, a feature not offered on factory replacement parts. Inner insert has been replaced with a high strength steel socket. Replaces factory plastic nylon insert. This steel insert greatly increases ball joint strength and durability. This is a must for lifted vehicles running an tire larger than stock applications. Ball and socket are assembled using an exclusive threaded preload system that insure precise tolerances for prolonged joint life and precise steering. Ball & shaft are constructed from industry leading SAE 4140 Chromolly steel. Combined with steel insert ensures that these ball joints are an industry leader in durability and strength.