These units are generally used in conjunction with shrink or stretch wrap machines. They all work on the same basic principle in that the product is received on a conveyor either in single or multiple lanes and collation for a single tier takes place progressively along a conveyor in a horizontal plane. When loading into trays it is usual for the tray to be fed under the machine at a slight angle where the required collation is separated from the main stream of product and located in the tray by "hitting" the front edge of the tray and is progressively loaded into the tray. The trays can be manually erected or automatically on a tray erector before feeding into the machine.

Cans, bottles and other round objects all follow the same principle. Cartons are collated in a similar manner but care has to be taken as regards the direction of travel as cartons can fall over.

Generally it is far more difficult to collate and load when the product is more than one high.

Tiering units which automatically place one filled tray on top of another can be supplied and installed just before the shrink/stretch wrap machinery.