An improved file for use in the endodontic preparation of a root canal, the file having a handle portion at one end and an active working portion tapering toward the distal end, the active portion having an external surface with at least one helical flute forming a helical scraping edge and, preferably, an axially adjacent land, the working portion having areas or zones of reduced surfaces that contact root canal surfaces during use. Preferably the zones are a plurality of axially spaced zones of reduced diameter so that the total length of file working portion in contact with canal wall surfaces during use is reduced. In manufacturing the improved file, a plurality of axially spaced zones of reduced diameter are formed on the working portion of a conventional file, including helical flutes and lands as desired, wherein the file of the invention includes an undulating external working portion profile.