Late in 1913, Sundback introduced his "Hookless Fastener," based on novel principles and resembling in all important respects the modern metal zipper.
Sundback's hookless fastener depended on the action of a series of closely spaced elements, technically called "scoops," whose precise spacing and ingenious shape are key to the fastener's success.
The fastener consists of two opposing rows of scoops, spaced so that the scoops from one side engage in the spaces between the scoops on the other side.
More generically called a "slide fastener," the zipper is used as a closure in garments and a variety of other articles.
Zippers were first introduced in a primitive form in the 1890s, but were not widely accepted in clothing until the 1930s.
The nib from one scoop fits into the dimple in the facing scoop, whose nib in turn fits into the next dimple down the row.
Trained as an electrical engineer, Sundback was a remarkably clever and astute mechanic.
He analyzed with care the key elements of the automatic hook-and-eye, and concluded that the hook-and-eye model was not a suitable one for any kind of automatic fastener.