Official Answer
Answer
When installing an internal retaining ring deep within a housing, the bore must have a lead-in chamfer (typically $15^∘$ to $20^∘$ and at least 1.5 times the ring thickness in length). This chamfer acts as a natural compressor for the ring. Without a proper chamfer, the sharp edge of the ring will catch on the bore entrance, causing the ring to 'cock' and potentially scoring the precision-honed surface of the bore. In hydraulic systems, this scoring can create leak paths for high-pressure fluid. The chamfer should be smooth and free of burrs to ensure the ring slides effortlessly to its destination groove.
