Cornerstone 2 inch Tow Bar Adapter Part # March 04, 2018, 11:11:25 am Have a 2016 Cornerstone and need manufacturer and part number to drop down to a 2in tow bar. The Cornerstone has a larger square hole to tow up to 20,000 lbs and I need to find the adapter to down size to 2 inches. Thanks for your help.Take careBillFound one on Amazon. Reese Super Titan Receiver Adapter. 3 inch to 2 inch adapter sleeve.