I designed this for a New Era 59Fifty hat which has a flatter brim, but didn't have one around when I printed it out. So I tried it on my coworkers 39Thirty hat, also by New Era, that has a much more bent brim but it worked just fine. You need to push it as far as you can onto the brim to make sure it is tightly on there. Once I did this I couldn't shake it off, with GoPro attached. It is made to fit the clip that all the other attachment connect with, not the frame itself. As of now the arms are relatively thin so let me know if anyone has one break on them and I'll go back and thicken them up.