The connector in question is at the end of a Waters ESI probe used in conjunction with a Waters G2S spectrometer. The connector is on a RG 58 C/U MIL C-17 cable and is of the push pull variety (does not thread into spectrometer). I was looking at BNC male connectors, RP BNC female connector, and also SMB jacks as they seem to have an indentation ring around their outer casing just as the connector in question does. The pin in the center has a diameter of 1mm. Let me know if additional measurements are needed. Thanks in advance!