together the rings thereby fit snugly together to form a substantially continuous resilient sleeve on the outside of the casing extension 9 the segmented sleeve 12 may therefore be provided to any desired depth on the casing extension the uppermost ring 13 a overlaps the profile 7 and is shaped on its inside to conform to the profile 7 the inner flanges 15 may be bonded to the extension 9 the thickness of the sleeve may be in the range of 15 35 mm in the example the sleeve 12 has an outside diameter of 18 u2033 457 mm and an inner diameter of 14 u2033 356 mm the conductor housing 2 is pre tensioned by means of a tensioning device 17 in which as described in gb patent no 2393990 and u s pat no 7 025 145 movement of an operating member 18 causes outward oblique movement of a driving ring 19 and thereby tensioning of the housing 2 within the casing extension 9 is disposed a production casing 20 extending downwardly from and supported by a casing hanger 21 in this example the production casing has a 10 75 u2033 273 05 mm outside diameter the annular space 22 defined at its inner periphery by the production casing and at its outer periphery by the casing.