The present invention provides a setting tool having a tubular sleeve assembly. An upper mandrel is disposed within said sleeve assembly and interconnected therewith by a rotational screw jack means. A lower mandrel is connected to the upper mandrel by a load transfer device for governing a maximum downward force which can be applied to the lower mandrel when the setting tool is set down on a packer. The load transfer means includes a casing connected to the upper mandrel, said casing having a support surface for engagement with an upper end of a packer mandrel. Resilient spring means is provided between the casing and the lower mandrel, and is constructed so that when said support surface is in engagement with said packer mandrel, a downward force applied to said lower mandrel must be transmitted through said resilient spring means. The maximum downward force which can be applied to the lower mandrel, and correspondingly to a sliding sleeve of the packer, is equal to a force required to fully compress said resilient spring means. Also, an improved releasable locking means is provided between the upper mandrel and the sleeve assembly so that the sleeve assembly may be released to allow free rotational and axial motion of the upper mandrel relative to the sleeve assembly.