a system for securing a member , such as a shelf , to a vertical support column and holding the member in a desired position on the column includes a rotary sleeve system whose resistance to downward motion is directly proportional to the downward force applied . a conical frustum shaped collar having an integral pin extending inwardly from its inside surface rests on top of a split conical frustum shaped sleeve having configurations in the split to receive the pin in one of two positions , an unlocked position and a locked position . a horizontal portion of the slit may be provided for restricting downward motion of the collar with respect to the sleeve to maintain the split in an open configuration , allowing free movement of the rotary sleeve system up or down the vertical column .