This is a very practical device. In the old days, we use to mark the tube with a file, add water to reduce the surface tension, say a prayer and winkThe glass cutter can be used for teaching or personal use, you should pay attention to avoid cutting yourself when using. If the head that is worn out needs to be replaced, so as not to affect the useThis tube cutter is designed to mark the circumference of the tube. It will mark the borosilicate and flint glass, produce a very clean break.Diameter of the glass tube can be cut to (approx) 4.5cm. Please note that the item could not cut the glass tube totally, just cut one way, then you shower the item with cold and hot water alternately, so that the glass tube will break