Well, for extra large corks! You can see where Pandanus spiralis gets its name from.
The spirals on the trunk are the bases of the old leaves that have fallen off. Most species of Pandanus grow like that but not many leave the old leaf stubs so prominently. Before the old leaves fall they they cling to the trunk in whats' called a "skirt".
Because the leaves are prickly on the margins, the skirts create a defensive shelter for many small animals. There are a good couple of hundred on my place. They look great but you have to be careful when working near them. The leaf margin prickles are really sharp and really cling when they catch you.