Sorry, I forgot to answer your question about the hose size - based on the picture of your old one, the female flare size is 3/8 like the ad you show from Amazon. The black plastic part that screws onto the outside threads on the propane cylinder is almost always the problem because there is a shoulder inside of it that hits the end of the cylinder valve before it depresses the safety inside the cylinders' opd valve. If you use a brass P.O.L. fitting instead it will always screw in far enough to depress the safety inside the OPD valve. This is what I'm talking about using instead: https://www.amazon.com/Mr-Heater-4-Inch-Restricted-fitting/dp/B001SGUVJU/ref=sr_1_4?ie=UTF8&qid=1492808454&sr=8-4&keywords=brass+pol+fitting