The only way to fit a modern multi-speed cassette hub is to spread the rear of the frame from its original 113 mm to 130 mm. The inside of the seat stay has to be scalloped away for chain clearance. The lower part of the stay must be flush with the inner surface of the drop out. A portion of the tube has been removed with an angle grinder. The resulting void has been filled and reinforced by brazing in a 3 mm thick piece of steel plate. The flatted part of the stay is therefore effectively solid - and stronger than it was to start with.