Official Answer
Answer
The edge margin is the distance between the groove and the end of the shaft or bore. If the edge margin is too small, the housing material will fail in shear or 'blow out' when the ring is loaded axially. The required edge margin $z$ is typically calculated as $z = \frac{3 \cdot P}{\pi \cdot D \cdot \sigma_y}$, where $P$ is the thrust load and $\sigma_y$ is the yield strength of the housing material. A general guideline for steel housings is an edge margin of $3 \cdot d$ (three times the groove depth), while for aluminum housings, $4 \cdot d$ or $5 \cdot d$ is recommended. Failure to provide sufficient edge margin will lead to a catastrophic failure of the assembly, even if the retaining ring itself is intact.
