Abstract: A casing for a shell- and tube-type heat exchanger is produced by deforming two axially spaced portions of a length of tubing to make their integral peripheries either larger than or smaller than the internal periphery of an intermediate portion of the casing which is interposed between the end portions. A tubestack comprising tube elements supported by tubeplates is received within the casing, with the tubeplates being disposed at least partially within the end portions respectively. In the case where the natural bore of the tubing (which forms the internal periphery of the intermediate casing portion) is accurately sized and one of the end portions has a larger internal periphery than said bore, transverse baffles of the tubestack can have external peripheries which are accurately sized to engage the internal periphery of the intermediate casing portion. Otherwise, the baffles can have flexible tires mounted on their peripheries to engage the internal periphery of the intermediate casing portion.