Spherical Washer Sets allow the top and bottom halves to adjust to compensate for uneven or mismatched surfaces, achieving a flat bolting surface. A set consists of a female half (concave) where the washer is hollowed out or curved inward, while the male portion is convex (bulging outwards). These two halves match for a perfect set. The thickness of the set is calculated by putting both halves together and measuring the overall thickness. Both halves are machined and turned on our machines from 12L14 Low Carbon Steel. Parts are then case hardened, which hardens only the top layer of steel, leaving the center soft - this imparts strength on the bearing surface, but allows the part itself to flex, and avoid cracking from being too brittle. A Black Oxide plating is then applied, for appearance and a corrosion inhibitor. Made in the USA.