【正文】 he edge of the material being sewn. There may be many variations within this class, incorporating from one to four threads, only one of which is needle thread. They are generally used to neaten the cut edge of a single ply of fabric or to seam or neaten the edge of two plies in one operation – particularly in knitwear since this stitch configuration has excellent stretch and recovery properties when sewn with suitable threads. The needle thread determines strength, while the looper threads are chosen for best appearance and softness. Also in this class are a number of stitch types, which incorporate three or four threads, two of which are needle threads. The second needle thread, being further from the cut edge, gives greater security to the seam pared to the single needle version. As the looper thread runs between the two needle threads under the fabric these seams also have good extensibility.Stitch Class 600 Covering Stitch (Flat Seam Stitch)The stitch types in this class utilise between two and four needle threads, generally one looper thread and one or two cover threads. The cover threads(s) lie on the top surface, held down by the needle threads and the looper thread(s) interloop with all the needle threads under the fabric as in stitch type 607 illustrated.All these stitches are highly elastic and product flat, fortable, good wearing seams joining pieces of material, which butt together but do not overlap. For this reason, the looper and cover threads must be chosen to give seam strength as well as a soft handle. They are often called covering stitches and the most plex, employing four needle threads, one covering stitches and the most plex, employing four needle threads, one covering thread and four looper threads is known as Flatlock stitch and has the best security to its class.Stitch Class 700 Single Thread Lockstitch This class of stitch is formed with a single continuous needlethread and has for a general characteristic that at the penetration of the first stitch a portion of the needlethread is wound onto a reel in the lower mechanism of the machine. The stitches are formed by interlacing the needlethread with the thread wound on the reel. The interlacing of this stitch class, except for the initial stitch, is identical to that of Stitch class 300.Stitch Class 800 Combination Stitch This class of stitch is formed with rows of stitch types from two or more different stitch classes sewn simultaneously, at a specified distance from the edge of material and a specified distance from the edge of the material and a specified distance from each other.49 / 49Seam FormationDefinition:A seam is a joint consisting of a sequence of stitches uniting two of more pieces of material and is used for assembling parts in production of sew items.Classification:Seams are divided into 4 classes, within each of which there are several types of seam. The characteristics of each class are indicated in below:a) Class SS (Superimposed) This class of seam has for a general characteristic that the plies of material are superimposed and joined with one or more rows of stitches.b) Class LS (Lapped) This class of seam has for a general characteristic that the plies of material are lapped and jointed with one or more rows of stitches.c) Class BS (Bound)This class of seam has for a general characteristic that it is formed by folding a binding strip over the edge of one or more plies of material and joining the plies and binding strip with one or more rows of stitches.d) Class FS (Flat)This class of seam has for a general characteristic that it is formed by uniting the abutted edges of material in such a manner that the stitches extend across and cover, or tends to cover, the edge or edges of the plies joined.StitchingDefinition:Stitching consists of a sequence of stitches for finishing on edge or for ornamental purposes or both, in preparing parts in assembling.Classification:Stitching are divided into classes, within each of which there are several types of stitching. The characteristics of each class are indicated in below:a) Class OS (Ornamental)This class of stitching has for a general characteristic that a series of stitches are embodied in a material either in a straight line, a curve or following a design for ornamental purposes.b) Class EF (Edge Finishing)This class of stitching has for a general characteristic that series of stitches are formed at or over the edge of the material, the edge being either folded or not folded, or that the edge of the material is folded and joined to the body of the material with a series of stitches.