> Yes the offset vanes stiffen the spider for rotation but > now the vanes are not in line so you now have 8 weaker diffraction > spikes instead of 4 stronger spikes. ???? No, we still have 4 spikes with offset vanes. They may be not "in line", bit they are parallel. Also, offset doesn't just increase axial torsional rigidity - it increases _overal_ rigidity as well. Bratislav