An effective pair potential reduces the dipole-dipole interactions in a polar fluid to spherically symmetric form. In this way it is shown that the Stockmayer model of polar fluids can be reduced for weak to moderately strong polar interactions to a Lennard-Jones form wherein the potential parameters are temperature dependent, Bulk properties and surface tension can then be obtained by standard simple fluid methods. The generalized van der Waals theory is used to calculate the surface tension of hydrogen halide single-component fluids (HCl, HBr, and HI).