A pallet, sometimes inaccurately called a skid (a skid has no bottom deck boards), is a flat transport structure that supports goods in a stable fashion while being lifted by a forklift or pallet jack. A pallet is the structural foundation of a unit load which allows handling and storage efficiencies. Goods or shipping containers are often placed on a pallet secured with strapping, stretch wrap or shrink wrap and shipped. Since its invention in the twentieth century, its use has dramatically supplanted older forms of crating like the wooden box and the wooden barrel, as it works well with modern packaging like cardboard boxes and Intermodal containers commonly used for bulk shipping.

Pallets Construction

Wooden pallets typically consist of three or four stringers that support several deckboards, on top of which goods are placed. In a pallet measurement the first number is the stringer length and the second is the deckboard length. Square or nearly square pallets help a load resist tipping.

• Two-way pallets are designed to be lifted by the deckboards. The standard North American pallet, or GMA pallet, has deckboards of 40 inches and stringers of 48 inches.
• Four-way pallets, or pallets for heavy loads (or general-purpose systems that might have heavy loads) are best lifted by their more rigid stringers.

Although pallets may be fabricated to various custom sizes, there are some typical sizes that are most commonly used. Of the top pallets used in North America, the most commonly used by far is the Grocery Manufacturers' Association (GMA) 48x40 inches pallet, which accounts for 30% of all new wood pallets produced in the United States.

There are six pallet sizes recognized by ISO. Here is a list, including the region most commonly used:

Due to the International Plant Protection Convention (abbreviated IPPC), most pallets shipped across national borders must be made of materials that are incapable of being a carrier of invasive species of insects and plant diseases. The standards for these pallets are specified in ISPM 15.

Pallets made of raw, untreated wood are not compliant with ISPM 15. To be compliant the pallets (or other wood packaging material) must meet debarked standards, and must be treated by the following means under the supervision of an approved agency:

• Heat treatment - the wood must be heated to achieve a minimum core temperature of 56 °C (132.8 °F) for at least 30 minutes. Pallets treated via this method bear the initials HT near the IPPC logo.

Pallet Types

• Stringer pallets 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.
• Block pallets are typically stronger than stringer pallets. 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.

Reference: http://en.wikipedia.org/wiki/Pallet