Hello Oldman, we're sorry to hear you are experiencing trouble attaching this to your propane tank. You can connect the fitting of the hose/regulator assembly to the cylinder outlet without an adapter. Just turn the fitting counterclockwise into the threads of the cylinder valve. Some models have a hand wheel that can be slid off the nut so that a wrench can be used to tighten the fitting, if desired. If you need additional assistance, we're happy to help! Just reach out by phone at 877-447-4768 or email here: http://www.ghpgroupinc.com/CTUS.html
-GHP Group Customer Support