  The mass flow conductance of single nanoholes with diameter ranging from 75
to 100 nm was measured using mass spectrometry. For all nanoholes, a smooth
crossover is observed between single-particle statistical flow (effusion) and
the collective viscous flow emanating from the formation of a continuum. This
crossover is shown to occur when the gas mean free path matches the size of the
nanohole diameter. As a consequence of the pinhole geometry, the breakdown of
the Poiseuille approximation is observed in the power-law temperature exponent
of the measured conductance.
