Also known as a pallet truck, pallet pump, or pump trucks, pallet jacks are most commonly used in warehouses and storage facilities owing to their easy transportation of pallets. Pedestrian operated trucks have forks that slide beneath pallets and use a hydraulic jack to lift the load from the ground for transportation. Pallet jacks are limited by their maximum height and so are suited for moving loads from the ground or low level. For greater height of lift, a reach truck is necessary. These forklift trucks are able to extend their forks beyond the cab to reach into warehouse racks as high as 12m. The usually have very low ground-clearance and so are often unsuitable for outdoor work.