While in the past violin strings were made of sheep guts, today many violin strings are commonly made of wound steel. Only the highest pitch string (E string) is made of unwound steel. The other three: G, D, and A are made of wound steel. All strings, at their ends, are wound with cotton threads to protect them from wear and tear. The cotton thread also provides friction to keep the tension in the string. It is possible to observe the marks showing the wounding of the steel strings on the right side of the images shown below.