Opening is designed to hold securely on the smallest scape as well as the largest.
Extra Fine point Industrial Model Sharpies are available at most office supply stores. For your convenience they are also available at Northern Exposure. Development required me to order in extremely large quantities, which allows me to make these available to other AHS hybridizers. For me this has been the perfect tagging system. Some hybridizers have found that it supplements their existing system because they always carry a few in their pocket for that spontaneous cross.