Summoners War - Rune - Grindstone

Grindstones is a Special Rune type item that can be obtain randomly in the Scenario Map - Rift of Worlds when defeating a Raid boss. There's many different Grindstones, because it exist a Grindstones for each Rune Set. When using a Grindstones, it increase a Sub-Stat on the same Rune Set of the Grindstones! It exist 5 different Grades of Grindstones: Common, Magic, Rare, Hero and Legendary!

We can use as many Grindstones we want on a particular Rune, the increased value is base on the Grindstones and they are in a Range, like 2 to 5%, so if we use a Grindstones with +2 to 5% ATK on a Rune with a ATK% Sub-Stat of 8, it can become 10 to 13%, if we get the minimum 2% we can re-try later with another Grindstones to try to get more then +2%!

Rune Grindstone Available

Grindstones
Available	ATK+ / ATK+% / DEF+ / DEF+% / HP+ / HP+% / SPD
Not Available	Accuracy+% / CRI Dmg+% / CRI Rate+% / Resistance+%

Rune Grindstone Grade

Grade Available in Rift of Worlds
Normal (R1-R2)
Magic (R1-R3)
Rare (R2-R5)
Hero (R3-R5)
Legendary (R4-R5)

Rune Grindstone Min/Max

Grindstones	Magic	Rare	Hero	Legend
ATK+% / DEF+% / HP+%	2-5	3-6	4-7	5-10
ATK+ / DEF+	6-12	10-18	12-22	18-30
HP+	100-200	180-250	230-450	430-550
SPD+	1-2	2-3	3-4	4-5