A thermal transpiration flow through a single rectangular micro-channel was studied experimentally for various gas species, including all rare gases, in order to investigate the influence of gas species on the flow properties. The final equilibrium flow characteristics and relaxation time of the pressure variation were evaluated as functions of the rarefaction parameter. The thermal molecular pressure difference was well fitted by the log-normal distribution function, and its magnitude was found to be strongly dependent on the gas species: a larger pressure difference was obtained for molecules of smaller diameter. However, for the thermal molecular pressure ratio and the thermal molecular pressure exponent, which are dimensionless quantities, the dependence on the gas species was negligible. The relaxation time of the pressure variation was well normalized by the characteristic time of the system. The influence of the geometry was evaluated by comparing the present results, obtained for the case of a rectangular channel, with already published data obtained for the case of a circular cross-section tube. The comparison showed that these two geometrical configurations influence the fluid flow in equal manner, if appropriate geometrical parameters are used for their representation.