A rail threading mechanism for a rail handling vehicle includes a thread box mounted on the outer end of a manipulating arm. The thread box includes a platform and a pair of jaws pivotally connected to the platform and moveable between open and closed positions. The platform includes a support roller for rollingly engaging the flat bottom of a rail. Each jaw include a plurality of jaw rollers positioned for rollingly engaging a rail positioned on the support roller when the respective jaw is in the closed position. The jaw rollers on each jaw preferably include a pair of base rollers positioned for engaging an edge of the base of the rail, a pair of flange top rollers positioned for engaging a top surface of the top flange of the rail, and a flange side roller positioned for engaging an edge surface of the top flange of the rail.