Split pin nose pads were probably the best option for most antique eyeglass frames that supported the nose pad arm with a 1 and 1/2 mm square hole . These nose pads allowed ease of changing and did not require much thought or experience to perform. The split post that rises up from the base of the nose pad could easily be split apart by the tip of a flat head screwdriver. This allowed the post to fold over metal opening, bending outwards. The final adjustment to secure the nose pad would be by using a small needle nose pliers to bend the metal flap completely outwards and squeezing them close to the nose pad arm to eliminate any chance that it may snag something and bend out of place, which could loosen the nose pad in its position.
As with the age of ever changing eyeglass frames and improvements on different aspects such as nose pad mounts, hinges, and more, eventually those manufacturers who created these frames and replacement parts make the decision to discontinue them. Which is the case here with the split pin nose pads. These nose pads were used on various antique eyeglass frames, such as American Optical and others. Eyeglass frame manufacturers who used to use this type of nose pad mount, which have kept making these frames(or newer versions), have made changes to newer mount types to keep the image alive without having their frames go the way of the Dodo as well
The picture above shows another similar mount nose pad alongside of the split pin nose pad. They both have a similar size post, yet one is solid and the other parts down the middle. The square pin nose pad is also unfortunately retired.