A sliding‐shaft type of vacuum lock for a mass spectrometer is described in which the sample carriage and pumping manifold are made entirely of sintered alumina (95% Al2O3). The hardness of this material effectively eliminates any problem of seizing due to entrance of foreign matter or gradual wear of the bearing surfaces. Components of the high voltage ion source are fully insulated when mounted directly on the carriage. The single ended design avoids the critical alignment required with two‐manifold systems.