Retaining Rings work by creating a shoulder that can hold components in place. The retaining shoulder is created when the ring attaches itself to the bore or shaft, typically by snapping into a groove. Ordinarily (however not always) a groove is dug into the shaft or bore, and this groove becomes the seat for the retaining ring. Retaining rings are designed such that their contact diameter has some interference fit with the groove in which they fit. This creates a “snug” fit between the ring and groove. The term used to describe the amount of interference fit is “cling”.
Cling causes the retaining ring to fit tightly and securely against its groove bottom. Without cling a ring would have a loose fit and would “rattle” in its groove. This lack of cling would decrease the retention capacity of the ring because a “cling-less” ring is free to move radially, creating weak retention points that will ultimately cause the assembly to fail. Another key factor is the width of the groove. The groove width is slightly larger than the rings thickness, thus creating a snug axial fit. The tight axial fit along with the cling to the groove bottom creates a rigid shoulder which can retain thrust loads. ¹⁾

The phrase “Retaining Ring” is sort of vague and refers broadly over several different types of retaining fasteners. Some names used include: snap rings, wire rings, circlips, lock rings, retainer clips, retainer rings among others. For our purposes, Internal or External are the main words to remember since the rings are machined different for both types of use. Rings for bores are referred to as internal retaining rings, because the ring fits inside a hole (or bore). Similarly rings that fit over shafts are referred to as external retaining rings, because the are installed on the outside (or external) side of a shaft.

External retaining rings are made smaller than (to expand and place on a shaft or) the groove cut into a shaft while internal retaining rings are sized bigger than the intended groove / resting place to compress and install. External Snap rings are axial retaining rings and are installed into a groove in a shaft or bore along an axis center point. Axial rings have lugs and lug holes that are used for installation. Once installed, they contact virtually the entire groove. They transmit loads into the groove wall around most of the groove circumference, which lets them withstand significant thrust loadings. ²⁾

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Internal retaining rings are made bigger in diameter than external snap rings to compress into a groove in a housing.

(AKA, Eaton-style or horseshoe snap ring). ⁴⁾

It features a uniform, constant section. This means that the material used to make the ring is the same width at any point along the circumference of the ring.
These can be bought from fastener companies in carbon steel as plain or with oil embedded.

There are no known pliers to compress the ring due to it having no holes or slots for pliers.
So it was pried out with screwdrivers in a circle pattern to get the ring out of the groove in the pivot.
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