Sprung W-irons using piano wire as the spring. Designed for any 4mm scale 4- or 6-wheeled carriage (14mm diameter wheels) irrespective of the mass of the carriage; the only adjustment required is the selection of the most suitable wire material and or diameter (0.011″ supplied) to give the required ride height. Best used with waisted bearings. Full instructions included. Sufficient for three 4-wheeled or two 6-wheeled carriages.