English: Cross section and plan of the connection between a water tube and chamber in a Reed water tube boiler. The end of the tube is threaded, and a ferrule with a convex hemispherical profile is screwed onto it. The end of the tube is then inserted into a hole with a concave hemispherical profile and of slightly larger diameter in the wall of a water chamber and secured with a nut on the inside of the chamber. The hemispherical profiles and the diameter of the hole allow for slight variations in fitting tubes. "[T]hough they have been many times under steam, not a single leak has occurred."(Anon., "Reed's water-tube boilers", The Engineer, 14 February 1896, p. 172)