If a ring moves about too much, a bar could be better. In a BCR, a ball has two dimples, which the ends of the ring grip. The ball can be changed for other shapes. Barbells have a ball at each end, one of which screws on. It needs no special equipment.
Some people stretch their piercings, to get larger jewellery through.
The most usual material is surgical stainless steel. UV-glow plastic is fun in discos. Again, about half the customers do not have piercings of the publicly visible sort. Punk types with earloads of ironmongery are a tiny minority. Navel piercings are most popular at the moment.