Mojo's Blackjack Double Penetration C-Ring. Simple and super sexy in design, a super smooth, sexily swollen probe will be positioned perfectly for a smooth anal entrance once two stretchy silicone rings are in place around your, your partner, or your dildo's shaft and balls. The rings are nice and snug without being uncomfortable. They are more for probe support than erection support, though they will help with that, too. Material Silicone. The Blackjack's rings stretch from about 1.5 inches and 2 inches in diameter. Overall length 6 inches, insertable 5.5 inches.