The Vault Daleks (or Crucible Daleks) were a subset of Daleks unique to the New Dalek Empire possessing a specialized manipulator arm. They were charged with guarding their creator Davros in the Vault, a special chamber within their giant space station the Crucible.
Like every individual Dalek of the New Dalek Empire, the Vault Daleks were created from a single cell of Davros' body. However, they differed from the other New Daleks on account of their special type of manipulator arm: a claw possessing eight pincers, to access special hardware within the Vault. They were tasked by the New Empire's leader, the Supreme One, to keep watch over their creator Davros inside the Vault.