The SPRiT MX Economy Springs have a slightly reduced precision rate, at 98% instead of 99.5%. This equates to roughly a +1g/-1g variance in the weight (compared to 0.3g variance with 99.5% precision), and one screening of spring performance per batch instead of the usual two.
These are great cost effective options if extreme precision isn't desired. Slow Extreme II Economy will be available later, the below options are now in stock. Each pack comes with 100 springs.
63.5 Supreme Economy
63.5 SLOW Extreme I Economy