These are SPRiT Slow Extreme II springs, made of high quality stainless steel. Available in 55g, 60g, 63.5g, 65g, 68g, 72g & 78g weights, each pack comes with 100 springs.
The Slow Extreme II are about 3-4g heavier at the start compared to the Slow Extreme I version. See below information from SPRiT on the different spring weights and force curve graph for different spring types.
Force Curve Graph