Samoon Powerful Recoil Spring For GHK M4 GBB Airsoft Rifle
Tempered high-carbon steel Construction Airsoft Spring
Suitable For GHK M4 GBB Rifle Airsoft Gun

** Piano wire, or music wire, is a specialized type of wire made to become springs or (as the name implies) to be used as piano strings.
It is made from tempered high-carbon steel, also known as spring steel, which replaced iron as the material starting in 1834.
Piano wire has a very high tensile strength to cope with the heavy demands placed upon piano strings; accordingly, piano wire is also used for a number of other purposes, including springs, surgical uses, and in special effects. **