Simpson’s uterine sound is a somewhat rigid rod, flexible before introduction, and provided with a corrugated handle as above described.  Typically about eleven inches in length, the shaft being graduated in inches and quarters.  A slight knob formed in the distal end of the shaft denotes the average normal depth of the uterus.  The tip is expands into a rounded bulb to avoid perforation of the fundus.   1899 Truax.