Suction and increased blood flow to the nipples can increase sensitivity and improve circulation. The Size Matters See-Tru Nipple Boosters enlarge and stimulate using gentle suction. Simply place them over the nipple and squeeze the bulb to create a mild yet effective vacuum. Once you let go, these fun nipple toys will stay in place on their own. With the see through chamber, you get to watch all the action as you play! Size total length 2.5 inches, diameter 1.25 inches at widest point.