A gantry (10) includes a telescopic support rail (15) which comprises an outer member (20) and an inner member (22) each having an upper surface. The inner member (22) is telescopically movable relative to the outer member (20) so as to project from one end of it. The inner member (22) also comprises two spaced-apart wheels (30, 32), and a chain of links (38) forming part of an endless chain (36) that extends around the two wheels (30, 32), one link (38a) being fixed to the end of the outer member (20), such that the links (38) along the top of the inner member (22) define a substantially continuous surface (43) aligned with the upper surface (42) of the outer member (20).
