the engagement unit 7a with its slide 8a down to the box 1b and by then making use of the end face 4b as an engagement surface when a suction cup 5a is used to move the load the load may be for instance a common plastic or cardboard box it is possible with modern suction cups to achieve high degrees of vacuum and therefore load engagement surfaces need not be perfectly smooth or even there must merely be an accessible engagement surface the size of the suction cup is so that vacuum pressure will be maintained without rapid leakage instead of a single suction cup several suction cups may be used when handling big loads if the suction cup 5a is one that aligns itself with the load the engagement surfaces 4a and 4b need not themselves be perfectly aligned for engagement a self aligning suction cup may for instance be constructed with a pivot in the arm of the suction cup 5a in that case the suction cup 5a will align itself properly with the engagement surface so that the vacuum required for engagement of the load can be obtained it is often advantageous when moving the boxes 1a and 1b onto the conveyor 3a and onto the shelves 2a and 2b or vice versa to position the conveyor 3a to be slightly higher than shelves 2a or 2b making the boxes 1a or 1b thereby easier to move in this case as the box 1a or 1b is being pulled from the respective shelf 2a or 2b it is at the same time lifted with the aid of the suction cup 5a so as not to foul the edge of the conveyor 3a it is also.