After use the blocks are re-oiled or greased to protect against corrosion. The ability for a given gauge block to wring is called wringability; it is officially defined as "the ability of two surfaces to adhere tightly to each other in the absence of external means." The minimum conditions for wringability are a surface finish of 1 microinch (0.025 µm) AA or better, and a flatness of at least 5 µin (0.13 µm).[3]