The PRD Series of roller screws from Exlar, Minneapolis (www.exlar.com), are stand-alone devices that convert rotary torque into linear motion and last 15 times longer than similarly sized ball screws. This is possible because roller screws have more contact points than ball screws, thus the PRS series also has higher stiffness and more load capacity than comparably sized ball screws. With diameters from 3.5 to 150 mm, it carries loads up to 779,000 lbf for thousands of hours. Standard lead accuracy is 23 mm/300 mm. It accepts input speeds up to 5,000 rpm, resists shocks, and is available with and without center or end flanges. An optional preloaded nut reduces backlash to zero, and the device makes minimal noise, according to Exlar, which suggest the roller screws are ideal for demanding, continuous-duty applications.