outer ends of the screw shafts the adjustment screw shafts pass through drilled passages in two plastic laminate end members 54 and are secured to the deckle seal member 48 by locknuts 56 on the opposite sides of such seal members as shown in fig2 thus rotation of the handles 52 causes rotation of the adjustment screw shafts 50 which slides the deckle seal members 48 toward and away from the end member 54 in order to adjust the lateral position of the deckle members the deckle member 48 slides across a support plate 58 of metal which is fastened by bolts 60 to the bottom of the end member 54 and forms a vacuum seal with such support plate to prevent pressure leaks between the deckle member 48 and the end member 54 in one example of the present invention having a suction box cover with an overall length across the conveyor belt of about 280 34 twenty nine of the cross braces 34 each 1 5 34 high 0 5 34 wide and 13 5 34 long were provided equally spaced 8 34 apart with the space between the two deckle members 48 varying between about 241 34 and 246 34 in this example the ceramic cover strips 22 were about 0 625 34 wide 0 437 34 high and 251 63 34 long while the drainage slots 20 between such strips were approximately 0 750 34 wide eleven of the suction box cover elements 14 were employed in this cover so that the width of.