Ostomy bag coupling

An ostomy bag assembly comprises a bag and a fitment secured around the stoma the bag having a coupling in the form of a neck with an annular lip 17 which is insertable in a deformable collar 24 in the fitment. A resilient ring 50 embraces the collar and has projecting tabs 54 and 55 by which it can be tightened to deform the collar about the neck of the bag coupling. A ratchet mechanism is provided whereby notches 60 and 61 in the ring are shaped to receive a tooth 58 on a tongue 56. The ring is so sized that when the tooth engages notch 60 no significant pressure is applied to the collar but, on squeezing of the tabs, the tongue is pushed further through aperture 59 until the tooth engages notch 61 thereby locking the ring in its tightened state and deforming the collar inwardly.