Yale's other significant invention is the Chilled Iron Bank Doors and Vaults. Previous bank doors, vaults, and safes had plates of hard cast behind soft wrought iron, which can be easily broken using the right amount of leverage and skillful vault-picking. The hard casts are often rigid and fragile, and susceptible to heavy tinkering. Yale used a lattice screen, or basketwork of soft, tough wrought iron, instead of the hard cast, infused in the metal covering of the vaults, thus producing incomparably strong corners and surfaces that Yale presented to be unbreakable.