commonly referred to as a hospital stretcher it will be seen that the same has a base frame 10 comprising an elongated central channel member 12 from which post like members 14 extend from opposite end portions of the channel 12 such structure is of conventional type and functions to support a bed like member 16 which receives and supports a human body extending transversely from opposite ends of the central channel 12 are end frame members 18 the opposite ends of which respectively support caster assemblies 20 it also will be seen from fig2 that the end frame members 18 when considered in conjunction with the central channel 12 generally define a rectangular frame and the caster assemblies 20 are mounted respectively in the so called corners of said frame which may be considered as defining the corners of a rectangular pattern of position of said casters it will be seen particularly from fig2 that the caster assemblies 20 actually comprise two pairs of longitudinally spaced casters respectively disposed at opposite sides of the composite frame 12 18 as viewed in fig2 the upper pair of caster assemblies 20 along one side are freely swivelled relative to the ends of the frame members 18 while the opposite pair of longitudinally spaced caster assemblies shown along the lower portion of frame 12 comprise coupled casters and these are associated with the present invention further referring to fig2 it will be seen that a longitudinal housing 22 having a smooth upper surface also is provided with downwardly extending opposite side flanges to form a cover for an endless flexible member 24 which in accordance with the preferred embodiment of the invention comprises a sprocket.