The first major difference between pallets is material. Pallets can be made from a variety of woods and synthetic materials. I have never encountered a synthetic pallet but I have seen just about every other kind of pallet. They can be made from pine, poplar, oak, hickory or any other kind of wood. Pallet makers usually use smaller trees so anything not used for lumber can be cut up and made into pallets.
- There are two types of lumber pallets, those marked HT and those marked MB. HT pallets are heat treated to kill pests and make them safe for use. MB pallets are treated with chemicals. Most countries outside the US require pallets to be HT, heat treated. HT pallets are usually made of a high quality wood such as red oak, cherry or black walnut that is too small or low quality for other uses. Which means HT shipping pallets are a great source of high quality project lumber, if you take the time to reclaim it.
Another big difference is the dimensions of the lumber. Remember, the manufacturer is using smaller, cast off trees to make these the pallets. For the most part lumber is cut into standard dimensions but it is very rough. Some pallets are made for heavier loads and are built with larger pieces, some are built for light loads. The boards used for the packing surface can also vary in width. Depending on the project it could take a significant amount of time to find and fabricate the right pallets.
There is no standard size pallets for building with. They are made to suit the needs of the manufacturers and the clients who buy them. Pallets are made for different purposes and different products. If your project relies on whole pallets or standard sizes of cut up pallets then it could be difficult for you to achieve your goals. It is possible. Finding a steady source of pallets is a good place to start. Pallets will probably come from the same source on a regular basis which increases your chances accumulating enough pallets. You may also be able to find a large number of the same pallets in one place. Large shippers may have dozens of pallets from the same source. Other than that it just takes time to find the right pallet. Whenever I break one down for parts I save whatever I can. I sort the pieces by type of wood and when I have enough I make something.