Timber mats are commonly used for temporary or portable road ways, bridge decking, excavation support, crane pads and pipeline construction. Timber mats usually are made of planks, which can be oak, mixed hardwoods, Douglas fir, or man-made materials. The timber mats must withstand large forces such as the weight of heavy trucks and machinery positioned or moving on top of them, and so must be supportive and secure. To attach the planks securely together, metal rods or bolts are generally driven through the planks.