N.Y.C. Admin. Code § 27-693: § 27-693 Minimum section.

Except as provided in article ten of this subchapter for timber piles, no tapered pile shall be less than six inches in diameter at any section, nor have less than an eight inch diameter at cutoff. The taper of any tapered section may be uniform or may occur in steps. No pile of uniform section shall have a diameter of less than eight inches, or, if not circular, a dimension of less than seven and one-half inches. Tapered shoes or points of lesser dimensions may be attached to the tips of piles.