Curtis Universal advises customers to put boots on their ball and pin universal joints when operating conditions are harsh. That is, where materials like abrasives or chemicals can shorten the lives of moving parts. The boots are flexible polymer covers for the joints. The company stocks a standard line of Neoprene covers, and takes special orders for joints booted with EPDM, silicone, or Viton fluoroelastomer. Neoprene, a DuPont synthetic rubber, is resilient, resists abrasion, tearing, and flame, and generally is unaffected by moderate chemicals, fats, grease, and many oils and solvents. Curtis recommends its U-joints for applications where misalignment exceeds 3 degrees, where torque is high and variable, or where the angle of misalignment changes during operation.