In some embodiments, a nuclear magnetic resonance (NMR) sample container having an elongated transverse cross-section is held in a predetermined azimuthal orientation in an NMR probe by keying-in a sample container holder into a matching azimuthal-alignment adapter. The azimuthal-alignment adapter may be a lead-in adapter having an azimuthally-sloping upper guiding surface of a cylindrical shell part, with the sloping guiding surface leading into a longitudinal channel defined through the shell wall. A transversely-protruding pin of the sample container holder slides down the guiding surface and into the longitudinal channel to lock the sample in the desired azimuthal orientation.