They generally have a usable hair-length of around 65 cm, and the balance point is 19 cm from the frog. The bows were elegantly fluted through half, or sometimes the whole, of their length. The curve in the wood was created by heating the wood thoroughly and then bending it. Before Tourte, bows had been cut to the desired bend. The final important change credited to Tourte is the screw in the nut to moderate the tension in the hair. This propelling and withdrawing screw is found on virtually all modern violin bows. He is also credited with the invention of the spreader block, which fixes the hair of the bow in a flat ribbon, and so prevents tangling.