A slide positioner for moving a structural member from an inoperating position to a working or operating position has a square shaft for supporting the structural member. Two bearing assemblies are adapted for supporting the sliding shaft. The two bearing assemblies are spaced one from the other and are connected to a stationary base. One of the bearing assemblies is rigidly connected to a pneumatic cylinder whose piston rod is connected to the sliding shaft. The bearing assemblies are mountable to the base in various angular positions since the bearing assemblies may be pivoted around an axis which is parallel to the axis of the sliding shaft.