These are SPRiT Slow Extreme II springs, made of high quality stainless steel. Available in 63.5g & 68g weights, each pack comes with 100 springs.
See below information from SPRiT on the different spring weights and force curve graph for different spring types.
SPRiT Slow Extreme II
63.5S - Starts at 44g, slow force increase
68S - Starts at 47g, slow force increase
Force Curve Graph