Suction and increased blood flow to the nipples can increase sensitivity and improve circulation. The 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 the action as you play. Measures 2.5 in. total length 1.25 in. diameter at widest point.