Abstract: A pretensioning device for causing an automatic line splice to exert a strong grip on the ends of two cables inserted into opposite ends of the automatic line splice. The pretensioning device has a rack supported for sliding movement in a rectangular tube. The rack has a series of teeth along its length. A sled mounted on the rectangular tube has a dog engageable with any one of the teeth on the rack. A cam on the rectangular tube is provided for moving the sled lengthwise of the rectangular tube while the dog engages a tooth of the rack to extend the rack. A clamp on the rectangular tube grips one of the cables and a clamp on the rack grips the other cable.