A simplified fluid-mechanics model is developed for the drawing of silica capillaries. Calculations are carried out to predict the influence of the technical parameters on the final geometry of the capillaries. Geometrical collapse is inevitable when drawing capillaries, and active control of the parameters only helps to some extent in tuning the final structures. Drawing experiments were performed to check the theoretical calcualtions. Good agreement was obtained, which certified the validity of the model. The predictions provide valuable practical information for the fabrication of photonic crystal fibers.