In coils of up to 15 tons, the tank top should be dunnaged with two double lines of 6"x1" (15cm x 2.5cm) dunnage wood boards. For coils of over 15 tons, three lines of such dunnage should be used. In order to achieve tight stowage and prevent movement, wooden chocks must be inserted on top of the lines of dunnage in the lower tier.