Abstract: A pair of like rails are secured to a vehicle roof regardless the curvature of the roof surface at the rails to the plane of the roof between the rails. Two pairs of stanchions to which a corresponding crossbar is secured are slidably secured to the rails and slid into the desired position along the rails. The stanchions have a groove and surface defining a space in which a rail tongue having a circular end surface and an opposing rail circular surface are located to form a pivot arrangement forming a stanchion-rail pivot axis. The stanchion is formed of two members which are pivotally secured about an axis spaced from the rail pivot axis with a clamping knob located between the spaced pivot axes. The knob urges the members together and to the rail to form a tight clamping action to preclude the stanchions from sliding along the rails in response to wind and cargo loads.