The big round tip is a solid disk 24mm diameter. It is very useful for placing, to create circular disk shapes like planets, moons or bubbles. It can be used effectively with the small round tip too, allowing flower centers, variety in cosmic skies, fantasy images, etc. By sliding the big round disk you can create wonderful pipes, bamboo, etc. It is threaded to fit the encaustic art Stylus Pro wax graphics tool. There is a smaller version available too.