Surgical scalpels consist of two parts, a blade and a handle. In medical applications, each blade is only used once (even if just for a single, small cut). The handle is also known as a "B.P. handle" The handle of medical scalpels come in two sizes #3 and #4 handles. A #4 handle is larger than a #3. Blades are manufactured with a corresponding fitment size so that they fit on only one size handle