One of the most sought after antique golf clubs, the Spalding Kro-Flite double waterfall F-6 backspin iron has a wavy pattern of large, corrugated grooves on its face.   

Offered only in Spalding's October 5, 1919, catalog, this club was covered under the April 20, 1920, U.S. patent (No. 1,337,958) applied for on August 23, 1919, by William F. F. Reach.  According to his patent, Reach designed his double waterfall iron with deep grooves surrounded by a solid solid border. The grooves were of “wave line form” so they would impart “a backward spin to the ball whether struck by the direct or cut shot...stroke.” Reach defined the cut shot as “when the club is drawn across the ball at an angle to the line of play.”

The back of this iron is marked with Spalding's Crow & Kro-flite Trademark and "W. Strachan”, Special” and “Patent Apld For" The sole is stamped "F-6 Mashie Niblic." The 37” shaft and leather wrap grip are original. This is a fine example of this distinctive iron.

TCA2 Vol 1, p. 274-275.