To prepare catgut, workers clean the small intestines, free them from any fat, and steep them in water. Then they scrape off the external membrane with a blunt knife, and steep the intestines again for some time in potassium hydroxide. Then they smooth and equalize the intestines by drawing them out. Lean animals yield the toughest gut. Next, they twist the prepared gut strands together to make string. String diameter is determined by the thickness of the individual guts, and by the number used. A thin string, such as a violin E, uses only three or four guts, whereas a double bass string may use twenty or more. After twisting and drying, workers polish the strings to the required diameter.