There is disclosed a fluid adapter 200 for a breathable gas delivery device, such as a facemask (62, Fig 1), for delivering breathable gas to a user. The fluid adapter 200 comprises an adapter body 202 defining an adapter chamber 214； a pressurised gas inlet port 208 in fluid communication with the adapter chamber 214 and arranged to be fluidically coupled to a source of pressurised breathable gas (80, Fig 1) and an ambient air inlet port 204 arranged to provide fluid communication between the adapter chamber 214 and ambient air outside of the fluid adapter 200. The adapter 200 also comprises an adapter outlet port 210 in fluid communication with the adapter chamber 214 and arranged to be fluidically coupled to a delivery device gas inlet port 208 of the breathable gas delivery device 80； and an adapter connector 218 arranged to connect the fluid adapter 200 to the breathable gas delivery device 62 such that the adapter outlet port 210 is fluidically coupled to the delivery device gas inlet port 208. The device includes a rotatable part 206 comprising an annular 224 member and a moveable fluid port 208. In another aspect an indexing feature defining a plurality of discrete angular positions is described.
