The greatest challenge with root lengths of 16 mm or less lies with establishing and maintaining accurate working lengths. Many commonly used endodontic files are manufactured with 16 mm of working flutes, generally referred to as the “working portion” of the file (Fig. 2). All working portions are manufactured with a rate of taper, which is the change in file diameter over its length. Silicone file stoppers, used to establish and maintain working length, are manufactured to fit snuggly on the non-working portion of the file, corresponding to its largest diameter. When the stopper is positioned on an area of decreased file diameter, the result is a loose fitting file stopper (Fig. 3).