Prestolok fittings and A-LOK fittings are excellent for leak-free operation. The only more secure method would be to just weld the pipes together! These fittings are available in a variety of materials from steel and brass to aluminum and copper, as well as in ISO and ANSI threads.
Because A-LOK fittings instrumentation and analyzer applications require high degrees of reliability and accuracy, the standard material they’re made from is heat code traceable 316 stainless steel, though other materials are available.
You also get a huge variety of fitting types, whether you need to connect to male or female pipes, port connectors, or barb fittings.