This is 1.5" PVC pipe cut to a 15" length and slipped over the legs of a fold-up banquet table.
We determined the length of the pipes by measuring from the table top to my bent elbow above the table then added the length of the table leg that slipped into the pipe. Our first length was 18" and we cut it back to 15" once the pipes were put under the table. The table is about 2" below my waist. This height is recommended by ergonomic standards.
My lower back no longer hurts when working for extended periods of time.