In order to address the difficulty of quickly and safely installing power lines on transmission towers, a transmission tower line attachment device (150) is provided for facilitating installation of a line (180) on a hanging sheave (100). The line attachment device (150) comprises a first guide arm (152) and an upper frame (154) spaced from the first guide arm (152). The upper frame (154) defines a throat (156) between the first guide arm (152) and the upper frame (154). A resilient first gate (158) is arranged at an outer end of the upper frame (154) between the upper frame (154) and the first guide arm (152) and is adapted to open inwardly into the throat (156) in response to an external force and to close when the external force is removed. The line attachment device (150) is adapted to be mounted on the hanging sheave (100) at an inner end of the upper frame (154) and first guide arm (20).