My "flexi" was built using 2" maple, sized at 24" x 24". My upright support rods are 3/4"-10 threaded brass from McMaster-Carr, with all brass fittings - nuts, washers and top acorn nuts. For the spikes, I used Audio Points (model 2.0AP-1OINT). I have four shelves and a total height of 48 inches. The rack weighs in at around 300 lbs, and sits on a fiberglass reinforced concrete basement floor. Holes were cut in the maple using a 13/16" forstner bit. Rear legs offset toward center by 1" (each side) from the front legs, mainly to break up vibrations as a result of symmetry (think of a perfectly square listening room and the resulting sound - I believe the same problems occur on a much smaller scale vibrationally in a rack). I had prototyped several flexi models using steel rod and hardware, and several types of shelf material (furniture grade plywood, MDF, several composite laminates, etc) but found the thick maple to perform the best. I also believe brass to be one of the better metals to use in audio applications (there are numerous discussions online as to the relative merits of various metal types for audio use). Personally, I found that rubber-type damping materials either as through-hole bushings or as spacers between the washers dampened the sound to a degree I personally didn't care for, and seemed to detract from the overall dynamics of the system. Since I utilize brass Audio Points under all my components on the rack, the coupling/mechnical diode effects of the points seem to form a synergistic relationship with the rack itself, and measurable vibration seems nearly nonexistent. Of course, YMMV depending on existing substructure (wooden floors, etc), other types of isolation products already deployed, and personal taste. Happy building.
-Richard
