The raw materials of stretching spring occupy a very large share of the national musical instrument metal composite string and stainless steel wire.

Metal composite strings for national Musical Instruments: Strings for national Musical Instruments conform to ASTM-A228 or AMS5112... Stretch springs made of string wire of folk instruments are not recommended when the temperature is raised beyond 121 degrees Celsius (250 degrees Fahrenheit).

Tensile spring custom stainless steel wire: Stainless steel plate specification type 302, in accordance with ASTM-A313 or AMS5688, elastic yellow after heat treatment (only physical treatment) when the temperature increases above 260 degrees Celsius (500 degrees Fahrenheit), it is not recommended to use the tensile spring made of metal wire strings of national Musical Instruments. Specification Type 302 stainless steel plate slightly magnetic. The surface of the stainless steel plate has a little residual nickel, it is all normal condition, not easy to harm the product characteristics.