Never force a cylinder connection if it does not fit.
Our industry has developed standardized cylinder valve outlet and inlet connections, regulator connections, and transfer connections for specific types and groups of gases to prevent the misapplication of these potentially hazardous materials. Remember, if it does not fit, do not force it. Regulator connection threads must match those on the container valve outlet. These CGA standardized cylinder connections conform the Compressed Gas Association (CGA) standards.
Always examine a connection before use to ensure it is clean and undamaged. The container valve should be closed at all times, regardless of whether the cylinder is full or empty, except when it is in-use. Many styles of valves do not have handwheels. We have special wrenches available, including those designed for various size acetylene cylinders. Open the valve slowly and ensure it is pointed away from all personnel. If you have additional safety questions, please do not hesitate to contact us.
Source: CGA