The clamp I used for mine was also too big. So I used a rubber hose as spacer and cut it to fit. One has to tighten the clamp a lot and I also used some padding under my heavy Garmin Montana to rest on the dash board. That high thin bar transmits a lot or vibration to the GPS. The smaller the GPS and the closer it is to the bar, the less it will bounce up and down on rough roads

__________________
2014 XT660Z - Barrett pipe, DNA stage1.5, Barkbuster hand guards and handlebars, Pivot pegs, Teknik suspension, Guard-it engine protector combo, B&B rear rack, Trax topbox.