Abstract: A safety device for engagement to the rotary shaft of a spring-loaded overhead door assembly so as to cover an adjustable end of the coil spring which imparts counterbalancing torque to the shaft. The safety device includes a cup-like sheath having a generally cylindrical side wall and an end wall having an axial opening therein. A tubular sleeve extends from the end wall around the opening and a threaded passage is present in the sleeve. A threaded fastener is threaded into the passage, the fastener being recessed in the passage and having a head whose outer surface is uninterrupted except for a plurality of spaced-apart small holes whereby the fastener can only be rotated by a tool which is sized to fit in said passage and which has a plurality of prongs which register with said holes.