A plug for use in a counterbalancing mechanism of a cable-operated door. The plug is used for operatively connecting an overhead shaft to a torsion spring co-axially mounted thereon. The plug includes a cylindrical collar and a cylindrical flange. The cylindrical collar has opposite first and second portions and is provided with a hooking slot for hooking a free end of the torsion spring thereon, and the torsion spring having a segment coaxially mounted about the first portion of the collar. The cylindrical flange is rigidly affixed to the second portion of the collar and is used for transferring a torque between the torsion spring and the overhead shaft when the flange is securely fixed about the overhead shaft. The plug is characterized in that the collar is eccentrically mounted about the overhead shaft, thereby allowing the plug to be used when the radial space between the plug and the overhead shaft is limited and also preventing the overhead shaft from being damaged by the free end of the torsion spring.