Miniature ball screws in ABS automotive brakes rapidly open and close valves that apply and release fluid pressure to brake pads. This creates a pumping effect to help prevent brake lock-up. Aside from using wipers to prevent contaminant ingression, another way manufacturers increase reliability is with redundant load paths. An example of a load-path redundancy is the use of two or more circuits of balls within a ball nut. This increases reliability because if one circuit malfunctions the ball screw will continue to operate.
Screw threads with multiple starts also provide redundancy.
Double-start screws have two threads concentric with each other allowing independent circuits of balls to operate in each path. When multiple circuits are combined with double-start architecture, many redundancies are possible. For instance, two circuits in each of two starts produce four independent load paths. Aviation and aerospace applications often require ball screws with several redundant load paths. Although a ball screw's projected life drops with each lost circuit, structural integrity and function are preserved.