• Prerequisites: the earlier alteration lessons in this Part; Part II, Weight, drape, hand and stretch.
• Time: 45 minutes (knit taper) to 3 hours (jeans waist).
• Difficulty: moderate to advanced.
• Tools: stretch, ballpoint and jeans needles; topstitch thread; overlocker if you have one; hammer for denim seams; walking foot.

1. Remove the centre-back belt loop. Unpick the band for about 4 in (10 cm) each side of the centre back, inside and out.
2. Unpick the topstitching of the seat seam through the yoke.
3. Take in the centre-back seam through the yoke and seat, curving to nothing on the seat, as in Altering the waist: take in and let out.
4. Re-fell or overlock the seam, then topstitch two rows to match.
5. Cut the band at the centre back, shorten it by the same amount, and join with a seam.
6. Re-attach the band, topstitch, and replace the belt loop over the join.

Quick option for small amounts: two small darts under the back belt loops, each 1/4–3/8 in (6–10 mm), hidden by the loops. Teacher to check.

1. Mark the length on the wearer standing.
2. Cut, leaving 3/4–1 in (2–2.5 cm) for the hem.
3. Fold once (knits do not fray) and press lightly.
4. Sew from the right side with a twin needle, or with a coverstitch machine.
5. Stretch the hem gently after sewing; no stitches should break.

• Joggers with rib cuffs: shorten by unpicking the cuff, cutting the leg, and re-attaching the cuff, stretching it evenly.
• Jeans with stretch (2% elastane): may shrink less, but still wash before hemming new pairs.
• Coated or waxed denim: needle holes stay; take in only.
• Distressed or ripped jeans: reinforce rips near the seams before altering, or they spread.
• Maternity stretch panels: replace or extend with new jersey; see Part III, Pregnancy and postpartum.
• Left-handed: no difference; guide stretch cloth with both hands, without pulling.

• Do not pull stretch cloth while sewing; let the feed dogs move it. A walking foot helps.
• Test on the cut-off before sewing the trouser.
• Denim layers: slow speed at seams; turn the wheel by hand over the thickest part.
• Thread: polyester for stretch seams; cotton thread snaps.

• Women: high-stretch jeggings often gap at the back waist; a small centre-back take-in or elastic in the band works.
• Men: tapering jeans is the most common request; share it between seams if the change is large.
• Children: knit play trousers rarely need taking in; add knee patches and cuffs instead.
• Sportswear: flatlock seams on activewear are hard to copy at home; alter with an overlock and a coverstitch, or leave to a specialist.

1. Stretch-test every seam before finishing.
2. Take in a little less than pinned on stretch cloth.
3. Use woolly nylon in the bobbin for stretchy twin-needle hems.
4. Hammer denim seams flat before crossing them.
5. Use a hump jumper (or a folded card) behind the foot over thick seams.
6. Match the jeans thread: take a cut belt loop to the shop.
7. Lengthen the stitch for topstitching (3–3.5 mm); it looks more like the factory stitch.
8. Hide waist darts under belt loops.
9. Use spray starch or a strip of tissue under thin knits that get pulled into the needle plate.
10. Let knits rest after cutting; they relax back.
11. What professionals do differently: they keep a set of topstitch threads in the common jeans colours.

The seam pops when the wearer bends

1. Resew with a narrow zigzag or overlock.
2. Let out slightly at that point.
3. Prevention: never use a short straight stitch on knits.

The seam waves or stretches out

1. Steam it gently; most knits recover.
2. Resew with less pressure on the foot or a walking foot.
3. Prevention: do not pull the cloth while sewing.

Skipped stitches

1. Change to a ballpoint or stretch needle.
2. Re-thread the machine and check the needle is new.
3. Prevention: the right needle for the cloth.

The twin-needle hem tunnels (a ridge between the rows)

1. Loosen the upper tension slightly.
2. Add a strip of light knit interfacing in the hem.
3. Prevention: test on the cut-off first.

The jeans side seam swings forward after a taper

1. Take part of the taper from the inseam too.
2. Re-press the leg so the seams sit at the sides.
3. Prevention: limit outseam-only tapers.

The needle breaks on denim

1. Change to a jeans needle and slow down.
2. Hammer the seam flatter.
3. Prevention: hand-turn over the thickest layers.

The taken-in stretch trouser is too tight

1. Let out by half the amount.
2. Try a narrower seam allowance only at the tight point.
3. Prevention: take in less than you pin, and try on.

• Myth: stretch fabric fits everyone, so it never needs altering. Lengths and back waists still need work.
• Mistake: altering stretch exactly as woven (from the D&D ebook).
• Mistake: using cotton thread on knits.
• Mistake: mismatched topstitching on jeans.

1. Beginner: sew three seams on a knit scrap (straight, zigzag, overlock) and stretch them.
2. Improver: hem a pair of joggers with a twin needle.
3. Confident: taper a pair of jeans on both seams and re-fell the inseam.

As a hobby: once you can sew stretch, every pair of leggings and joggers can fit.

For earning: jeans tapering and hemming are among the most asked-for jobs; neat topstitching sells the work.

For teaching: the stretch test on three stitches is a quick, memorable demonstration.

• Wash stretch trousers cool and dry them away from heat, which damages elastane; see Washing and drying trousers by fabric.
• Press jeans topstitching from the wrong side to keep it raised.

• Do you choose the stitch by the cloth?
• Do you take in less on stretch cloth?
• Can you taper and re-fell a jeans seam?
• Can you hem a knit with a twin needle?

Quiz

1. Why does a straight stitch fail on knits? Answer: it cannot stretch, so it breaks or puckers.
2. Which jeans seam is easiest to taper? Answer: the outseam (side), usually overlocked.
3. Which needle for knits? Answer: ballpoint or stretch.

• Elastane (spandex, Lycra): the stretch fibre in blends.
• Twin needle: two needles making two parallel rows with a zigzag underneath.
• Coverstitch: a machine hem stitch for knits.
• Flat-felled seam: an enclosed seam with two rows of topstitching.
• Outseam: the side seam of jeans.

• Main source: D&D’s own trousers ebook, chapters 16, 25, 50 and 52 (stretch needs a stretch stitch; take in more conservatively), with general denim alteration practice.
• Stitch widths, lengths and needle sizes are starting points. Teacher to check on D&D’s machines.