Review on Enhance Your Device Setup: iBOLT Aluminum 17mm AMPs Adapter Plate for Garmin GPS, Smartphone Holders & More! by Mike Groover

I read the reviews with skepticism and wondered if I should even use the pair I ordered. When they arrived I was pleased to find a 100% metal block made up of a plate and ball and even has a small set screw that screws into the ball's shaft from the back of the plate. The diameter of the ball appears to be slightly smaller than the advertised 17mm, but is sufficient for most devices except for my Garmin Montana 650T. I will be ordering two more of these for my GPS friends and family.