This image is a construction of jacks. Each one of the thirty in the center cluster is tangent to four others and equidistant from a point in the center of the cluster. The individual ones that I added to give more of a 3D feel map directly to the location of one of the others in the center.
This is another piece that might be actually be fun to construct a real version of (the connected center part anyway) by welding together some oversized cast iron jacks.