I was able to get the helmet mount to work on my handlebar while I wait for the new mount I ordered. My bar is 31.8mm and the recommended replacement is rated for 32mm. I have a wrap on my handlebar which will affect sizing so I ordered a replacement mount that can accommodate a bar width that goes from 24 to 35 mm. My neck feels better today. I am fairly sure the culprit was the light on top of my head. I have three of those lights that I got in 2010 and they are a very good product. I may even ride after dark again this year. By the way, I ride 300 miles a week.