Figure 6-75.  Rotary hook. Figure 6-72.  Fourth step in forming a stitch. Figure 6-71.  Third step in forming a stitch. Figure 6-74.  Oscillating hook. Figure 6-73.  Fifth step in forming a stitch. The second type of machine is the “needle feed” machine.  With this type, the needle bar moves in addition to the feed dog  and helps move the material. This is a medium-duty machine.  The Brother B-791 is an example of a “needle feed” machine. The third type of machine is a “compound feed” machine.  This is a combination of the drop feed and needle feed along  with an alternating presser foot. This is a more positive feed  machine and is generally a medium-duty to heavy-duty  machine. The Juki LU-563 and Consew 733R are good  examples of “compound feed” machines. The needle is one of the smallest parts of the machine but is  probably the most important. It is the source of the perfect  stitch and also the most aggravation. The use of the correct  type and size of needle is most important in proper operation  of a sewing machine. Improper needles cause a machine to  produce poor stitching and may damage the material, or the  machine might not sew at all. Using the wrong needle can  and needle move up and down penetrating the material and  forming the stitch. This is generally the lightest duty of  machines. The Singer 31-15 and Mitsubishi DB-130 are two  examples of a drop feed. Needles 6-20