They use a frame of three or more parallel pieces of timber (called stringers). The top deckboards are then affixed to the stringers to create the pallet structure. Stringer pallets can have a notch cut into them allowing "four-way" entry. Forklifts can lift a stringer pallet from all four directions, though lifting by the stringers is more secure. Stringer pallets can be made of both wood and plastic. Block pallet Block pallets utilize both parallel and perpendicular stringers to better facilitate efficient handling. A block pallet is also known as a "four-way" pallet, since a pallet-jack may be used from any side to move it. Carrier block Carrier blocks are specialized pallets for lumber carriers Flush pallet Flush pallets are pallets with deck boards that are flush with the stringers and stringer boards along the ends and sides of the pallet. Perimeter base pallet All stringer and some block pallets have "unidirectional bases," i.e. bottom boards oriented in one direction. While automated handling equipment can be designed for this, often it can operate faster and more effectively if the bottom edges of a pallet have bottom boards oriented in both directions. For example, it may not need to turn a pallet to rack it, and operation is less sensitive to pallet orientation. Quality improvements The least expensive way to improve a pallet is usually to specify better nails. With non-wood pallets, a controlled coefficient of friction is often helpful to prevent the pallet from slipping from forks and racks. Stiffer pallets are more durable, and are handled more easily by automated equipment. If a pallet does not need to be lifted from all four sides, two-way pallets with unnotched stringers may be used, with the additional benefits of added rigidity and strength. Specifying tolerances on flatness and water content may help the supplier meet target requirements. Inspection of pallets, whether in person or by a third-party (such as "SPEQ" inspected pallets) offer additional assurance of quality. Manufacture The main processes that are used to manufacture wooden pallets: Material selection Cutting wood plate / block Chamfering (depends on the demand) Notching Nailing wooden pallet Plastic pallet Plastic pallets are often made of new HDPE or recycled PET (drink bottles). They are usually extremely durable, lasting for a hundred trips or more, and resist weathering, rot, chemicals and corrosion. The benefits of plastic pallets over wood pallets include the ability to be