This is a replacement spanner for Ground Control coilover kits.
This spanner is included only in certain GC coilover kits, so if your GC coilover kit did not include a spanner, then you do not need to buy this.
The most common misconception why people think they may need a spanner, is that they are tilting the car on its side to adjust the collars, so they are fighting the swaybars. The swaybars are designed to keep the car from tilting by pushing against the suspension, which makes it difficult to turn the adjuster by hand.
A spanner could easily ruin things if used under these conditions.
If this describes your situation, try lifting the front or rear of the car off the ground, and adjust with your hands.