A fitting for a fluid line that will contain pressurized fluid can include first and second fitting elements with respective sealing surfaces and an indicator element for indicating when a fluid seal has been formed. A fitting for a fluid line that will contain pressurized fluid can include first and second fitting elements with a sealing structure secured in one of the first and second fitting elements, wherein the sealing structure is axially resiliently compressible, one example of which includes a bellows element.