1.5 inches Nitrile C-Rings Rainbow from Spartacus Leathers. In response to the popularity of our rainbow pack of rubber cock rings, we have introduced a 5 pack in nitrile. Colorful, flexible nitrile cock rings are the perfect skin safe solution for those with rubber allergies, and they offer a firmer experience than our rubber rings. Colorful, flexible Nitrile cock rings from Spartacus are the perfect skin safe solution for those with rubber allergies, and they offer a firmer experience than our rubber rings. Categories: Bondage, Fetish, Kink, Love Rings, Classic Cock Rings, Men's Cock & Ball Gear. 2022.