Two Universal needles mounted on one shank create two rows of stitches simultaneously.  designed for hems and pintucks.
sizes relate to both distance between the two needles and thickness of the needle.  when selecting sizes always refer to your instruction manual for maxium stitch width.  Some basic machines have a 5mm width, which means you can't use the 6.0 needle.  Twin needles are not suitable for straight stitch only machines
 
Available sizes 1.6/80, 2.0/80, 2.5/80, 3.0/90, 4/90, 6/100