Abstract: On an upright support is an apparatus including a pair of relatively movable jaws between which a tubular frame member of a bicycle is securely clamped. One jaw has a rigid short sleeve terminating in a circular row of teeth adapted to mesh and lock with a similar circular row of teeth on the end of a rigid tube support in dentil fashion. Extending through the tube support is a shaft fixed to the short sleeve, which has a bushing bearing in the tube support. By a manually adjustable nut and screw device, the rows of teeth can be separated to enable the jaws to revolve thereby to position the bicycle in the most convenient work position. A manually adjustable nut and screw device enable the clamping jaws to be tightened or released.