There's a specific retaining ring used in some manufacturer's rear axle that pliers of that type are optimized for. I may own a pair, but, if so, I don't know why; I doubt I'll ever open up a rear axle.
I've owned piston ring expanders, and the set (pair?) I owned had little fingers above and below the seating for the ring ends, to capture the sides of the ring first; you would then carefully open the ring before inserting. As with so many tools I've had in my life, I got them after I no longer needed them.
Like Papaw, I just used my fingers: stuck my thumbnails into the gap, one on each end, while using my other fingers to hold the ring, and carefully open up the ring, trying not to scream as the sharp ends dug into the skin under my thumbnails. Worked fine. Sort of.
