modes of use no drawings for the simplified version are believed necessary in the simplified version only a single pair of guide posts 30 are provided for the plates 22 preferrably the pair shown adjacent the opposite ends of adjustable rail 23 although only the pair of posts 30 shown adjacent the fixed rail 24 could just as easily be used the two mounting plates 22 of the guide rail assembly are each provided with an enlarged opening 32 of the same cross sectional shape as the respective guide posts 30 so the two mounting plates 22 can engage over the posts slidingly with only a small clearance space existing between the posts 30 and the enlarged openings 32 this prevents lateral and longitudinal displacement of the guide rail assembly while allowing it to freely move up and down on the guide posts in this form of the table the mounting plates 22 are not provided with keyhole slots 31 extending from the two openings 32 since there are only two guide posts 30 and the guide rail assembly cannot be fixed at the top of those posts the tops of the two posts 30 may be provided with enlarged head portions or with screws 50 and washers having a diameter greater than the diameters of the openings 32 for retaining the mounting plates 22 of the guide rail assembly on the two posts the remaining structure of the guide rail assembly is.