Hurst self-feed air drill units Hurst Engineering offers self-feed drill units, which are preassembled and ready to mount. The units are comprised of standard "off-the-shelf" components. Various stroke length and configuration are available. Options include flow controls, limit valves, depth control, feed checks, foot pedal, linear positioning and more. The units are available with 1/2-, 3/4- and 1-hp.