These Nipple Suction Cups by Pumped will elongate, stimulate, and make your nipples sensitive.  They draw blood forward, filling the erect nipple.  Its increased pressure in the area stimulates your nerve endings.  Once released, the nipples are sensitive to touch.  These cups are great before or during sex, or even just to tease your nipples.  It comes in 3 sizes to choose from: small, medium, or large.  They are made with ABS plastic.  The small is 1.1 inches wide.  The medium is 1.6 inches wide.   The large is 2 inches wide.  Choose the cups that are wider than your nipple to leave space for suction.