the application for a drilling base as described above it is necessary to allow passage of the drill bit however for other applications this aperture 208 might not be required foot attachment means 110 u2032 are fixed to the foot plate 206 by rods 210 the attachment means 110 u2032 may comprise a suction arrangement provided with a suction port 112 u2032 similar to the embodiment described above with reference to fig4 and 5 the annular and foot plates 202 206 are fixed together by a rim element 212 that is provided with internal castellations 214 described further below the base plate 106 u2032 is received between the annular plate 202 and foot plate 206 and is sized so that when one edge 106 a touches the castellations of the rim 212 the opposite edge 106 b is still between the plates 202 206 around each internal periphery of the apertures 204 208 the annular plate 202 and the foot plate 206 are each provided with an annular o ring seal 220 thus between the annular plates 202 206 the rim 212 and the base plate 106 u2032 an annular or sickle shaped chamber 222 is defined the chamber 222 is filled with a rheological fluid which may be magnetorheological or electrorheological when the rheological fluid is liquid the base plate 106 u2032 is a close sliding fit between the plates 202 206.