I have used 1 1_2" PVC on my bean head.I was told that the taller the better,but too big pipe might be too stiff and might interfere with head flex.You use it whole,and hold it down sufficiently so that stems can't work in underneath.It works good by "tripping" the beans as they come off the sickle,and also then the reel gets an extra kick at them to push them toward the auger.