flats 60 thereon are placed against the undersides of the lower flanges 24 the lower flanges 24 have holes for the accommodation of the u bolts 62 so the bolts 62 are then inserted upwardly into the holes and the nuts 64 tightened thereon to anchor the shaft 56 in place in operation the roller 50 in fig4 as with the other rollers 50 and 46 are all free to rotate on their respective shafts 56 and 54 when maneuvering the crane 10 through various angles and also over different types of sloping terrain considerable thrust forces exist the function of the thrust washers 94a 94b is to prevent the rollers 46 and 50 from shifting against portions of the frame unit 16 more specifically against the webs 20 of the side beams 18a and 18b the friction and resulting heat will frequently distort or deform the integral flanges on the bushings that have been employed in the past while the same friction and heat can develop when using the separate thrust washers 94a 94b in contradistinction to the prior art integral flanges the rollers 46 and 50 are never prevented from rotating on their respective shafts 54 and 56 for the threaded dowel pins 97 will shear before any such happening occurs although the tapered boring of the rollers 46 and 50 in accordance with the teachings of my invention will be performed in.