>>966823Xuron 496 split ring pliers.
Before that, I used a knife, thumbnail, or screw driver (plus safety googles because they can fly pretty far!) Sometimes the parts you want to put together can wedge in and open it enough to slip on. The split ring pliers are a god send and you don't end up with flying split rings. I recommend everyone get one if they need to use split rings very often. Other brands have other built in "tools" along the jaws for crimping and cutting.
