Boeing control yoke hub for early-built B-17 Flying Fortress, 307 Stratoliner, YB-17 (Model 299) Plus more? Measures 3 1/4" in diameter. Late 1930s/early 1940s aluminum control yoke hub, part number 1 24586 aftermarket item. These "horn buttons" were held in place with four individual steel spring fingers, over which the cap was snapped into place. Made in the USA.