Grindstone Pentahydrate

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Grindstone Pentahydrate is an upgrade material in Arknights.

Item description
An advanced grindstone used in the finish machining of weapon parts. Can be used for a variety of upgrades and the synthesis of D32 Steel.

Compared to normal Grindstone, this tool has an even more stable structure. It is highly non-reactive.


The second of the Grindstone-type upgrade materials, Grindstone Pentahydrate is similar but much more stable and non-reactive, thus making it more useful and essential for Operator skill Mastery training and the Elite 2 promotion of 5★ and 6★ Operators.

Due to its stability, the Grindstone Pentahydrate is an important material for the synthesis of D32 Steel.



Grindstone Pentahydrates are available in:

  • Distinctions Store (sometimes) for 10 Distinction Certificate icon.png.
  • Headhunting Parametric Model Store for 75 Headhunting Parametric Model icon.png.

Special drops

Operation Sanity Drop rate
4-8 21 Very Rare (~5%)
7-17 21 Very Rare (~5%)
12-8 21 Rare
13-21 24 Rare


Product Material(s) LMD Morale Requires
Grindstone Pentahydrate.png
Oriron Cluster
Integrated Device
300 4 Level 3 Workshop


  • Pentahydrate is a suffix used for chemical compounds with five water molecules bound to it.

See also