A medical instrument configured to be inserted into a body cavity comprises a body comprises a first probe at a first end, the first probe comprising a first cylindrical portion with a first outer circumferential surface of a first diameter; a first circumferential edge at a distal end of the first probe; a first distal lip projecting outwardly from the first outer circumferential surface beyond the first circumferential edge and extending for at least a part of a circumference of the first circumferential edge; and a first marker lip projecting outwardly from the first outer circumferential surface and extending for at least a part of a circumference of the first outer circumferential surface; wherein the first distal lip is positioned distal to the first marker lip; and wherein the body comprises a hollow cavity to enable a second medical instrument to pass therethrough.