These are SPRiT Slow Extreme III springs, made of high quality stainless steel. Available in 63.5g & 68g weights, each pack comes with 100 springs.
The Slow Extreme III are about 3g heavier at the start compared to the Slow Extreme II version. They are also a little bit longer of a spring, about 19-20mm in length.
See below information from SPRiT on the different spring weights and force curve graph for different spring types.
Force Curve Graph