The present work connects transport properties of simple fluids flowing in nanochannels: the diffusion coefficient, the shear viscosity and the thermal conductivity. We used non-equilibrium molecular dynamics (NEMD) simulations of liquid argon flowing in a nanochannel formed by krypton walls, macroscopically equivalent to the planar Poiseuille flow, at constant temperature. All properties approach bulk values as the channel width increases. As the channel width decreases, the transport properties change dramatically: the diffusion coefficient decreases with the channel width, the shear viscosity increases with the channel width and the thermal conductivity increases with the channel width. The novel result of this work is that, if the size effect of one of the transport properties (say the diffusion coefficient) is known, then all the others can be estimated from results that apply to classic fluid mechanics.