Official Answer
Answer
The edge margin is the distance from the groove to the end of the shaft or housing. If this margin is too small, the material will fail in shear or 'blow out' before the ring or groove yields. The minimum edge margin $Y$ should be $3$ times the groove depth $d$. The shear area is $A = \pi D Y$. The blowout load capacity is $P_{bo} = A \cdot \tau_{yield}$. In subsea applications where high-pressure seals are retained by rings, an edge margin of $5d$ is often specified to ensure a high safety factor against catastrophic failure.
