Double (or Twin) NeedlesTwo needles on a cross-bar with a single shaft sews two lines of stitching at the same time. Can be used with zig-zag sewing machines that thread from front to back.Triple NeedlesThree needles on a cross bar with a single shaft sews three lines of stitching at the same time.Wing (or Hemstitch) NeedlesUsed for decorative stitching on tightly woven fabrics. The double hemstitch needle has one wing needle and one regular needle on a cross bar with a single shaft.Twin Needle NumbersTwin Needles are identified with two separate numbers such as 2.0/80. The 2.0 specifies the distance in millimeters between needles and the 80 is the needle size.