A trolley has a pair of front (18, 19) and a pair of rear (26, 27) wheels disposed symmetrically on a chassis (11) relative to a longitudinal axis (15) thereof for ground engaging rotation in a common plane. The chassis (11) incorporates a guide wheel (34) located intermediate the front (18, 19) and rear (26, 27) wheels for ground engaging rotation about a horizontal lateral axis (35) which axis is disposed at right angles to the longitudinal axis (15); a mounting for the guide wheel comprising an arm (36) having an inboard end (38), an outboard end (37) and a section (44) intermediate the inboard (38) and outboard (37) ends, the outboard end (37) bearing the wheel (34); the intermediate section (44) incorporating an attachment (39) to the chassis (11) enabling the guide wheel (34) to be displaced angularly about an axis (39) parallel to the lateral axis (35); resilient loading means (44) act to resiliently bias the guide wheel (34), by way of the mounting (36), downwardly into ground engagement in the common plane; and a raising means (49) for the guide wheel (34) acting by way of the mounting (36) such that, on the trolley being closely stacked with a similar trolley, the raising means (49) causes the guide wheel (34) to be raised out of ground engagement.