the side wall lower sections as shown in fig3 and 5 the side wall lower sections 26 28 are provided with holes 62 64 to receive fasteners for attachment of the lower sections to the respective air conveyor channel side walls 18 22 and with set screw holes 66 68 that are employed in vertically positioning the air conveyor flanges as will be explained the side wall lower sections 26 28 are attached to the air conveyor channel side walls 18 22 by threaded fasteners inserted through their respective fastener holes 62 64 as is done in the prior art air conveyor channel with the side wall lower sections attached to the air conveyor side walls a pair of mutually opposed longitudinally extending grooves 72 74 are defined between the side walls and their lower sections the grooves 72 74 receive the respective mutually opposed flanges 76 78 of the air conveyor channel in the same manner as prior art air conveyors with a longitudinal slot 80 defined between the flanges however the flanges 76 78 are not fixed in adjusted positions in the grooves 72 74 by set screws as was done in the prior art air conveyor instead the flanges 76 78 are free to slide laterally in their respective grooves 72 74 toward and away from each other on rounded ends of set screws threaded into the set screw holes 66 68 of the side wall lower sections 26 28 one representative flange 78 is shown in fig4 it being understood that the other flange 76 is basically the same as the one shown the flanges 76 78 are similar to prior.