The web states its 17mm for most Garmins upto about 7 inch screen size, after that the ball goes larger. I have just measured our 7 inch Garmin with a Mitutoyo vernier and the ball mount is 17mm .
Dave Plus Six "Squeak" Roadster departed. 1936 BSA Empire Star Q8. 1935 BSA W7-35. 1938 BSA M20
