The prop-hub for the 64 fits the 50. It's a tab shorter 2.050mm vs. 2.071mm. The 64 hub also needs the 64 prop bolt. I used this on my 50 in a Pitts before they started making a short hub for the 50. Worked just fine on the Pitts. Fit the cowling perfectly. This is an option if you don't want to wait for the short hub for the 50.