Guangzhou Naian Auto Part Co.,Ltd is the manufaturer for conventiional leaf spring,parabolic leaf spring, z-type leaf spirng, heavy duty trailer leaf spring. We have more than 10 years experiene in the field. All our leaf spring matearial are tested. The materil could be SUP7, SUP9, SUP11, it depends on the your demands. We have our onw design engineers to design new spring for you.