Hegar dilators were developed and introduced by Alfred Hegar in 1879 originally for use in the field of gynecology.[5] Typically, dilators are a set of metal rods of increasing diameters, from a few millimeters up to 26 millimeters. The rods are round, slightly curved, and have a conal tip. Some sets have conal tips at both ends, while others have one end flattened for easy handling.[6] Hegar dilators are typically marked with a Hegar number that is equivalent to its size in millimeters (e.g., a Hegar size 8 is 8 mm thick). Commercially available Hegar dilators are commonly sold in sets of 8, 10, or 14 individual rods.[7] Each set includes a range of sizes, popularly from 3 mm to 17 mm for single-ended dilators or 3 mm / 4 mm to 17 mm / 18 mm for double-ended dilators, though configurations with sizes anywhere from 1 mm to 26 mm do exist.[