Stitches

Length and width are starting points. Your cloth, needle, and thread will move the numbers. Test on a scrap of the same grain and the same number of layers. Write down what worked. Do not copy a magic number from a stranger’s machine onto yours and call it a rule.

Straight

The lockstitch. Two threads, a knot in the cloth. On a woven, it is the seam. On a knit, it is a risk: stretch the garment and the stitch stands still, then pops. Maven Patterns will allow a straight stitch on a stable knit if you sew under a little tension, and they warn you off it for swim and high-stretch jersey.

Starting length on a medium woven is often about 2.5 mm. Threads’ staystitching video uses about 2.5 mm for a holding row. Shorter (2.0) for stress and curves; longer (3.0 to 4.0) for basting or a topstitch that wants to show. Very short stitches perforate fine cloth and make ripping a cruelty.

Zigzag

The needle steps left and right. The stitch can stretch with the cloth, and it can bind a raw edge so a woven ravels less. Closet Core, for knit topstitch: length 2 mm and width 3 mm for a stretchy zigzag; length 2.5 and width 1.5 for a narrow “almost straight” zigzag on areas that will not stretch much. Victory Patterns: a construction zigzag on knits around 2.2 mm long and 1.5 mm wide; a wider 3 mm × 2.5 mm for understitching bulky knit bindings. Sew4Home shows a knit seam at 2.5 mm wide and 1.8 mm long, and notes some sewists prefer a wide zigzag that stands in for a serger.

Those numbers disagree slightly. That is the point. They are starting points. On a lightweight jersey, a wide zigzag can tunnel. On a ponte, a too-narrow zigzag looks like a straight stitch and then pops. Scrap first.

Three-step zigzag

Also called a tricot stitch on some machines: three short straight stitches out, three back, in a zigzag envelope. It is gentler on elastic and on knits that a single-throw zigzag would cut. NMSU Extension prefers a multiple-stitch zigzag on knits that need stretch in a hem finish, placed about ¼" from the edge. It is also a common stitch for applying elastic in lingerie. It is slower. It is harder to unpick than a plain zigzag. Use it where the cloth is delicate or the elastic would be sawed.

Stretch / lightning

A narrow lightning-bolt stitch built for seams that must stretch. Sew4Home: the stretch (tricot/lightning) stitch on their sample sat at width 2.0 and length 2.5, default. Closet Core: very stretchy, looks professional, nearly impossible to rip out, and a poor choice for topstitching elasticized openings because it can kill recovery. Maven: slower than zigzag, harder to unpick, do not stretch the fabric as you sew. If your machine has it, it is the construction seam for a T-shirt when you do not have a serger. If you think you will need to refit, zigzag instead.

Overlock and mock-overlock

A serger trims, sews, and finishes. Three-thread overlock neatens; four-thread sews a stronger seam with stretch. Maven: 3 threads for neatening, 4 or 5 for an all-in-one seam. Threads Magazine’s serger thread piece: match fiber and weight to the machine and the cloth, the loopers often want a finer thread than the needles.

Mock-overlock on a sewing machine is a wide zigzag or a dedicated overcast stitch along a raw edge, sometimes with an overcast foot. It does not trim. It does not replace a four-thread seam on a gym-legging. It keeps a woven from fraying in the wash. NMSU: zigzag ¼" from the edge on fabrics that ravel; multiple-stitch zigzag on knits that need give.

Blind hem

A few straight stitches in the hem allowance, then a bite into the garment fold. From the face you should see a dimple, not a drawing. NMSU describes the hand version: small horizontal bites, ¼ to ½" apart, catching a yarn of the face. Machine blind-hem wants a blind- hem foot and a test of width so the zigzag barely catches. Slightly looser upper tension keeps the bite from puckering. On knits, a stretch blind-hem (if your machine has it) or a narrow zigzag is kinder than a rigid straight blind-hem.

Buttonhole

A dense satin-stitch box, or a keyhole, around a slit. Interfacing behind the cloth is not optional on a bias or a knit; Threads’ Bias 101 says to stabilize buttonholes on bias with straight-grain interfacing in the direction of the hole. Length is the button’s diameter plus thickness, tested on a scrap of the same layers. Cut the slit after the stitching, from the center out, with an awl or a chisel, not through the bartack. If the cloth tunnels, widen the bite slightly or add a wash-away stabilizer on top.

Topstitch and edge-stitch

Topstitch is a visible row, often ¼" from an edge or seam, sometimes longer in stitch length so it reads as a line. Edge-stitch is the same idea, walking 1/16 to 1/8" from a finished edge. On wovens, a straight stitch in a matching or contrast thread. On knits, Closet Core’s menu: zigzag, lightning, triple zigzag, or a coverstitch / twin needle if you have it. A straight topstitch on a stretch hem is a pop waiting to happen, unless that hem never stretches (a full knit skirt, maybe).

Understitch

After you sew a facing, understitch is a row on the facing side, through facing and seam allowances, that keeps the facing from rolling to the outside. Threads, Norma Bucko: trim allowances to a scant ¼", clip every ½" staggering the clips, do not press yet. Facing right-side up, allowances toward the facing, stitch ⅛" from the seam. Keep the facing flat even if the garment bunches. Then press so the seam rolls to the inside. This is the difference between a neckline that sits and a neckline that winks.

Staystitch

A single row on one layer, inside the seam allowance, that keeps a curve or a bias edge from growing while you handle it. Threads: about 2 mm to 2.5 mm long, 1/16 to 1/8" outside the seamline (on a ⅝" allowance, stitch at ½"). Sew directionally, with the grain, usually from the high or wide end toward the low or narrow: shoulder to center on a neck, neck to armhole on a shoulder. Do not stretch the curve straight while you sew. Staystitching stays in the garment. It is not basting.

Basting

A long, temporary stitch, meant to come out. Machine basting is a long straight stitch (4 to 5 mm) with reduced tension so it pulls. Hand basting is a running stitch. Use it to hold a zipper, to ease a sleeve cap, to test a fit, to keep velvet from creeping. Do not backstitch. Do not staystitch with a basting length and then leave it, it will not hold a neck.

Wovens versus knits, in one pass

Tension and length as starting points

Upper tension on a home machine often sits around a mid number (4 on a 0 to 9 dial). That is a factory compromise, not a virtue. If the knot shows on the underside, the upper thread is too loose or not in the discs. If it shows on top, the upper is too tight or the bobbin path is dirty. Change one thing, sew a scrap, look at both sides.

Length: 2.5 mm is a reasonable lockstitch start on medium cloth. Shorter for curves and stress. Longer for basting and some topstitch. Width, on zigzag: start narrow for seams (around 1 to 1.5 mm in the Victory and Closet Core notes) and wider for finishes. None of these survive a needle that is too small for the thread, or a dull needle that makes a hole instead of a stitch.

Piecing a quilt is still a straight stitch, but the thread is 50 wt so the ¼" seam does not swell. all-purpose vs quilting. A T-shirt wants polyester all-purpose and a stitch that stretches. Same machine; different spool.