The use of the proper wood and crate fasteners will result in a container that offers maximum strength while using a minimum of materials. Woods are categorized based on their hardness or density and their weight:
- Group I — Softer woods with only moderate nail-holding capacity and moderate strength, but do not readily split when nailed.
- Group II — Heavier woods with greater nail-holding capacity, but more inclined to split when nailed.
- Group III — Medium density woods with approximately the same nail-holding capacity as Group II, but with less tendency to split when nailed.
- Group IV — The heaviest and hardest domestic woods have a great capacity to hold nails, but are very difficult to nail and often tend to split when nailed.
Other factors that will affect the strength of the wood used are any strength-reducing characteristics such as knots and cross grain, the moisture content of the wood, and the duration of the shipping time and any storage period before or after shipping.
Regardless of the wood used, much of the strength, durability and effectiveness of any crate will depend on the type of crate fastener used. Until recently, nails have been the fastener most commonly used in the construction of crates. Screws are also commonly used, primarily for fastening sides and ends to the base of the crate. Both nails and screws have their advantages and disadvantages. Scrail is another option and is faster and more efficient.