is used in a tube fitting of the type shown in fig2 the housing member 7 fits over sleeve 1 the housing member 7 has an axial passage which has differing diameters along its length the housing member 7 is threaded into the aperture which is to be connected by the quick coupling alternatively the housing member 7 may be part of fittings such as tees and elbows which are to be connected to tubing via quick coupling the housing member 7 has a shoulder 13 formed by the differing diameter of the axial passage through the member tube 4 butts against this shoulder and is sealed by sealing means 14 which is held by a second shoulder 15 when the tube 4 is under pressure it will be urged in the direction of arrow x because there is frictional contact between sleeve 1 and tube 4 sleeve 1 will be urged in the same direction the internal passage of the housing has chamfered portion 7 39 when the protuberances 6 meet portion 7 39 they will be forced inward clamping the tube 4 in place any increase in the force tending to cause the tube to move relative to the housing member will increase the gripping force of the fingers the gripping fingers 2 will remain clamped against tube 4.