The field configuration near the conductors of a helical wave guide is obtained from the solution of the spatial-wave equation for a developed helix. This solution is first obtained for the case of tape conductors and then adapted to elliptical (including circular) conductors by conformal transformation. By comparing this solution with that of a developed-sheath helix, the impedance, attenuation, and other parameters of a wire helix are deduced approximately. These are expressed as the product of the corresponding sheath-helix parameter times a proper correction factor depending on frequency, conductor size, and shape. The analysis is extended to the multifilar helix. The results of this analysis provide a means of calculating the attenuation of wire helices and of choosing optimum wire configurations in the design of helical wave guides.