Abstract: A connector element is described which is suitable for connecting together two components (2a, 2b) in a system which is likely to be subject to vibration. The connector element has an indicating mechanism which provides an easily visible effect to show whether or not the two components are mated. In one embodiment the edges (10a) of a spring (10) protrude from a recessed portion (18a) in a nut (18) at the end of the bolt to indicate the unmated condition. In another form the end of an indicating lever (110) protrudes from a slot (112) in an adjusting nut (180).