ProTaper® Universal nickel titanium rotary files are specially designed to instrument difficult, highly calcified, and severely curved root canals. The patented progressive taper, and advanced flute design provide the flexibility and efficiency to achieve consistent, successful cleaning and shaping when faced with these challenges. The shaping 1 and shaping 2 files have increasingly larger tapers over the length of their cutting blades allowing each instrument to engage, cut and prepare a specific area of the canal. Shaping File Number 1 or S-1 is designed to prepare the coronal one-third of a canal, whereas, Shaping File Number 2, or S-2, enlarges and prepares the middle one-third. Although both instruments optimally prepare the coronal two-thirds of a canal, they do progressively enlarge its apical one-third. The finishing files, or F1, F2, F3, F4 and F5 instruments, have been designed to optimally finish the apical one-third, they do subtly and progressively expand the shape in the middle one-third of the canal. Generally, only one finishing instrument is required to prepare the apical one-third of a canal and the one selected is based on the canal's curvature and cross-sectional diameter. The SX or Shaping X file is an accessory file and is used to optimally shape canals in shorter roots, relocate canals away from external root concavities, and to produce more shape, as desired, in the coronal aspects of canals in longer roots.