Up to 1975, PND dolphins utilized friction pipe piles to distribute high tension loads. With the introduction of the torsion dolphin in 1975 by principals of PND, pile fins were implemented to improve both torsional and frictional resistance. Although effective, this improvement lacked reliability; particularly when subjected to repeated loading. The SPIN FIN® pile, which was extensively tested and developed by PND throughout the 1980s, employs fins welded to pipe piles at an angle; thus, the pile actually "screws into" the ground during driving. As a result, pile pull-out capacity is greatly increased; especially under repeated failure loads. It is estimated that use of this development can produce an equivalent savings of $10,000 per pile; however, at one installation savings escalated to a total of $12,000 per pile.