A down hole well tool for installing a casing or liner in a well bore includes a tool unit and an expansion module for expansion of the casing or liner. The expansion module has at least two sets of rolling means arranged along an axial direction of the expansion module, and each set of rolling means is provided at an outer circumference of the expansion module. The diameter of the rolling means decreases at least between the two sets along the expansion module, providing the expansion module with a decreasing diameter in an axial down hole direction of the well bore.