Smaller size works well on cats and smaller dogs. 6mm opening. 18fr. Speculum is useful for passing stomach tube in the conscious patient. The speculum is held in check by the canine teeth going through the two large holes. A 3/8″ round hole through the center allows a stomach tube to pass through. By holding jaws firmly closed any chance of biting the tube is eliminated. The hardened blue nylon resists chewing and can be cold sterilized for reuse.