A guide track system for a tool that can be raised and lowered within a telescoping drilling rig tower is provided. The system includes parallel guide rails mounted on a fixed lower tower section and on a movable upper tower section of the drilling rig tower. The lower and upper guide rails are parallel...http://www.google.com/patents/US7828086?utm_source=gb-gplus-sharePatent US7828086 - Guide rail system for a telescoping mast on a drilling rig
