The Longfield™ 27 spline birfields are made out of 100% chromoly and are precision polished to remove any imperfections that may cause stress risers. The Longfield™ birfield housing is made out of forged 4340 chromoly steel. The internals of our Longfield™ birfields are made out of vacuum arc remelted 4340 chromoly steel and then dual heat-treated for superior strength. For Toyota pick up applications.
From Trail Tough