Garment Construction and Sewing Techniques
What this domain tests
This domain examines whether you can select the right stitch, seam, needle and machine setting for a fabric and garment component, and whether you can diagnose common sewing faults. Expect questions on stitch types, seam finishes, tension, pressing and component attachment.
Core rules and concepts
- Stitch classes: 301 lockstitch is the standard straight stitch; 401 chainstitch is used where stretch is needed; 504 three-thread overlock neatens edges and joins knits.
- Stitch density: 10–12 stitches per inch (about 2.5 mm stitch length) suits medium woven fabric; too few stitches weaken seams, too many perforate and pucker the fabric.
- Needle selection: 70/10 for lightweight fabrics, 80/12 for medium cotton and shirting, 90/14 or 100/16 for denim and heavy fabric. A blunt or wrong-size needle causes skipped stitches and needle marks.
- Seam types: plain seam pressed open; French seam for sheer or lightweight fabric with raw edges enclosed; flat-fell seam for durability on jeans and shirts; overlocked seam for knits and bulk production.
- Machine balance: correct tension forms the lockstitch interlock inside the fabric. Upper tension too tight pulls the bobbin thread to the top; too loose leaves loops underneath.
- Pressing: press each seam as sewn, then press open or flat. Pressing sets stitches; ironing slides the fabric and can distort it.
Worked example
A cotton poplin shirt requires a strong, neat side seam. Choose a plain seam with 1 cm allowance, 80/12 needle, 2.5 mm stitch length and 12 SPI, then overlock or pink the raw edges and press open. For a sheer voile blouse, choose a French seam: sew wrong sides together at 6 mm, trim to 3 mm, turn, stitch at 6 mm, enclosing the raw edge.
Traps that cost marks
- Adjusting stitch length to fix a tension fault; these are separate settings.
- Using a heavy needle on fine fabric and causing holes or puckering.
- Confusing pressing with ironing, or pressing a seam before it is sewn correctly.
- Recommending a French seam on a bulky fabric where the enclosed seam becomes too thick.