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