Optima Fixed Tip 23-375, this tip is used to simulate a large ball, which can be used for shading. This tip is currently available in 3/8" (shown here), 1/8", 1/4" and 5/8" curvatures (the diameter it would be if it were an actual sphere). Like all of our pen tips, it is polished to a mirror finish, and is designed to keep the heat off your hands.