It is finely manufactured from A class piano wire.
Very durable and strong. 
Irregular pitch coiling for enhanced performance.
Easy to install.
Every spring has gone through vigorous and Sophisticated quality tests from the moment a new design leaves the software drawing through to final mass production.
 
Please Note
When buying parts from Longbow BB Ltd, you confirm you have the required ability to install and tech your airsoft replica as required. 
Longbow BB Ltd do offer a paid for service option for us to look at your rifle and try to solve any issues you maybe having. 
We need to manage your expectations as we (Longbow BB Ltd) are unable to provide extensive hours of tech advice for parts purchased that have been installed by yourself. 
All parts are inspected before dispatch to ensure product quality.