The GAS filters are pre-assembled individually. Their blade springs are bent into working position and installed pairwise facing each other. The tips of the blades are bolted to a keystone. This way, the blade pairs remain bent and keep each other from snapping back. Each blade is bent by means of a bending tool, as shown in figure5.14. The tool forces the blade to stay at a curvature with a radius of 199.6mm. This way, a bent blade has almost its final shape, so that only little additional lateral compression is required to tune the GAS filter.