Doc Johnson Novelties Optimale Men's Sexual Health and Wellness line. Optimale C-Ring Thick 40mm Slate. For Extra Thick results, look no further than the Optimale 40mm C-Ring! Made of soft, stretchable silicone for easy use around the shaft or testicles, these cock rings are perfectly suited for creating the most optimal of erections, and prolonging ejaculation. Offered in three individual sizes: 35mm, 40mm, and 45mm; collect them all! Available in Black and Slate. Phthalate-free. Video. 18.