The Hegar dilator is a manual, probe-style instrument used to progressively dilate the uterine cervix. This variant has only one working end of a specified diameter. The smooth, slightly curved, and blunt tip is designed to minimize the risk of tissue trauma or perforation during insertion. The 4.0 mm size is a common intermediate size in a graduated set, used sequentially to carefully enlarge the cervical canal for gynecological procedures like curettage and diagnostic hysteroscopy.