The Longfield™ 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 axle shafts are also made out of 4340 chromoly steel. The internals of our Longfield™ birfields are made out of 4340 chromoly steel and heat-treated for superior strength.