Flow through rack is also known as gravity flow. These systems are a first-in first out inventory management method. It is ideal for supplying pallet or carton loads of SKU's for sorting and distribution operations and without interrupting order picking. Unit loads are placed on the skate wheels or conveyors at the entry end of the storage flow lane. The conveyor is pitched slightly to allow the load to flow to the exit end of the storage lane. Gravity and the unit load's weight also allow the load to flow to the exit end of the storage lane. When a load is removed from the exit end, the next unit load in the flow lane will move forward to the exit position. Utilization factor is 90%, and throughput volume is high. Another type of flow-through storage rack system is the air flow rack. These racks are similar to gravity flow racks except that air forced through tiny holes in the pallet rails is used to float the pallets for movement instead of skate wheels or roller conveyors. Air flow pallet rack has a unit load utilization factor or 90%, and stock rotation is FIFO. Normally, captive pallets or slave boards are required to ensure smooth flow on these systems. Here loads are supported to an incline to a gravity based movement of the loads within the rack via e.g. a gravity roller conveyor. The load is loaded at the higher end and unloaded at the lower end i.e. FIFO.