The replacement Nasal Pillows for the Opus 360 Nasal Pillow Mask come as a single pair in your desired size: small, medium, or large. All three sizes fit on either the Opus 360 Nasal Pillow Mask. By using anatomically-shaped pillows, you'll get an easy and comfortable fit with a premium seal. The contours in the new shape and design adapt well to your unique curves, giving you the coverage you're looking for. What's Included: 1 Pair of Nasal Pillows in Selected Size General Tips Section As of December 5th 2008, Fisher and Paykel has made several improvements to the design of the Opus 360 Nasal Pillow Mask. The silicone pillows are now designed with a contour shape that keeps the Silicone Seal off the upper lip. Where do I find the size? To find the size of the nasal pillow, hold the nasal pillow with the two small openings facing upright. Turn the nasal pillow to view the back of the cushion, or the area that faces downward when placed into the mask frame. In the middle of the nasal pillow, locate a large, embossed letter within a clear square. This letter represents the size of the nasal pillow. 400HC118, 400HC117, 400HC116