A baler knotter

 A baler knotter is a mechanism that wraps twine around a bale of hay and ties it so that it will stay together. It is a part of a mechanical baler. The baler knotter consists of needle for pulling the twine, a long arm that pushes it around the hay, and a mechanism that ties the knot. A baler knotter can produce single or double knots.

The first action of a baler knotter is for the needle to move the twine to a holder. This holds it in place so that a knife arm can cut the proper length. Then the twine is moved around the bale and towards a piece called the bill hook which pulls it into a knot. Often several spools of twine will be stored inside the baler so that the knotter will have sufficient supply to continuously tie bales over long periods of time.