These are silicone so retain body heat very well. Two different sizes, one larger one smaller. Perfect placement is at the base and tip of the shaft. Use lubrication for even stimulation and increased sensation. 

Small rings inner diameter is 39 mm/ 1.5" unstretched

Large rings inner diameter is 50 mm/ 2" unstretched

Available in white or black

Each ring is bipolar, using its own channel.