Official Answer
Answer
The groove wall must be as perpendicular to the shaft or bore axis as possible. If the groove wall is angled (tapered), the retaining ring will not have a flat surface to bear against. This creates a radial component of the axial force, which acts like a wedge, trying to push the ring out of the groove. Most standards specify a maximum out-of-squareness of $0.005$ inches per inch of groove depth. If the groove is machined with a standard end mill, the 'radius' at the bottom of the groove must be smaller than the 'radius' or 'chamfer' on the ring itself. In high-performance automotive differentials, the groove is often ground after heat treatment to ensure perfect squareness and depth, maximizing the thrust capacity of the spiral ring.
