Here's mine I did earlier this year. About 10mm thick, two different designs. I have around 300 miles on them now, and no signs of loosening. I used lock washers to prevent the screws from loosening. I also put a red mark on the screw, lock nut, washer and arm so I can make sure they are still lined up after time. :wink:
Pics and info: http://endless-sphere.com/forums/viewtopic.php?p=238273#p238273