there are various sizes of double needles, some close together, some 1/4"-3/8" apart...I've used double needles for stitching stained glass blocks- went ahead & sandwiched my blocks & quilted them as I stitched down the 'leading' black bias- then put them together *quilt as you go* method. worked out fine- it does give you a zigzag on the back- but the project I used it for was fine with that- my bobbin thread matched so well it wasn't really noticeable unless you really got close & inspected it- since they were kids quilts the kids don't care a bit.