I'm not sure where you are seeing the 1.1 inch measurement. From the Amazon listing for the adapter:
"The adapter can be attached to a steel, 1.5-inch exposed quill-type stem and, in case it doesn’t fit your bike, a thread-less adapter is also available (sold separately)."
http://www.amazon.com/gp/product/B00...SWAG4GJDGX1Q6G