To drag or transport of a sewing machine is crucial for sewing leather or thick fabric.

Said a very simplified way, the drag consists of some kind of extra support for the fabric that you are sewing it slide and not be stuck. Usually a foot or presser foot that presses the fabric and the drag while the machine sews.

If you've never stitched with one of these machines, you'll have to get used to that there are two presser. One rises and the other low, alternately, to convey the fabric. When things with a machine of double or triple drag, you'll notice a great improvement. Especially into thick fabrics, such as are used in upholstery.