Polyethylene terephthalate (PET) is one of two basic forms of polyester materials available in machinable stock shapes today. PET offers excellent wear resistance, low coefficient of friction, high flex modulus and superior dimensional stability. PET differs from PBT in that PBT has a lower strength and stiffness but this in turn increases the impact resistance of PBT. PET also has a higher glass transition temperature. Both however are susceptible to hot water or steam if operating above 140° F. Both PBT and PET retain more of their physical properties at elevated temperature when compared to Acetal and Nylon. Internal lubricants can be added to enhance the wear resistance and coefficient of friction when compared to unfilled versions or Delrin AF.