This morning, the hot 3-D printing stocks are coming under some selling pressure. The three leading stocks in the industry group are ExOne Co (NASDAQ:XONE), 3D Systems Corporation (NYSE:DDD), and Stratasys, Ltd. (NASDAQ:SSYS). All of these stocks continue to look weak on the intra-day charts. Day traders can watch for intra-day support on DDD stock around the $44.20 level. It should be noted that DDD has the highest volume so it will generally be the most liquid stock when day trading.