Stretch Knit vs Rigid Woven: Sewing Machine Settings Compared

A knit and a rigid woven are not two difficulty levels of the same fabric. They are two different engineering problems that happen to run through the same machine.

A woven is warp and weft interlaced at right angles: it stretches only on the bias, it frays, and it holds a crease. A knit is yarn looped into itself: it stretches in use, it recovers — or does not — and instead of fraying it ladders, one loop pulling the next out of the fabric. Everything the machine does to one is slightly wrong for the other.

Here are the settings that change, side by side, and the mechanism behind each one — because a setting copied without its reason is the same setting done wrong.

Why Does Fabric Structure Change the Settings?

Because the needle has to get through the material without damaging it, and the seam has to survive what the material does in wear.

• In a woven, the needle should part or cut cleanly between flat yarns, and the seam is a rigid structure sewn into a rigid structure.

• In a knit, the needle must push the loops aside rather than pierce them, and the seam must stretch with the fabric and come back — a seam that cannot extend simply breaks at the point where the fabric stops and the thread does not.

That second sentence is the whole article. Seven settings follow from it: needle point, needle construction, stitch class, thread, tension, feed and needle plate.

Which Needle for a Knit, and Which for a Rigid Woven?

For knits, SCHMETZ formalises a four-needle rule that is worth knowing exactly:

SCHMETZ’s own rule of thumb: the more elastic the material, the more suited the stretch needle — if in doubt, use the stretch needle. Skipped stitches on swimwear, silk jersey or anything with spandex in it are usually not a tension problem; they are a needle-shank-to-hook distance problem.

For rigid wovens the answer is the needle this series keeps returning to: the Jeans needle, medium ball point, reinforced blade, NM 70–110, which SCHMETZ rates for denim, twill, canvas and tarpaulin. The point is the same family as the Jersey needle — a ball point — but the blade is built for stacks that fight back.

Two rules apply to both columns. A needle that is too thick makes ugly holes even when the type is right — SCHMETZ says test on scrap, and so do we. And the ball point is not optional on a knit: a sharp point cuts loops, and a cut loop ladders the fabric.

Which Stitch Class, and Why Does Lockstitch Fail on Knits?

This is the setting people get wrong at the buying stage, not the adjustment stage.

A 301 lockstitch interlocks at a single point. Needle thread and bobbin thread bind at that one point, and the seam has essentially no extension. On a woven that is a virtue — it is why the lockstitch is the reference standard for woven construction: a small, flat, durable seam that presses cleanly and takes a crease.

On a knit it is a timed failure. The fabric extends in wear; the seam does not; the thread pops or the fabric ruptures along the stitch line. A 301 lockstitch is not a primary construction seam on a stretch knit — not because the machine is weak, but because the stitch geometry is wrong for the material.

What knits need is a stitch that interlocks along a length of thread, so the seam extends and recovers with the fabric:

Note the division of labour between the two looper machines, because they get confused constantly: an overlock works on the edge — it trims with a knife and wraps the edge in the same pass. A coverstitch works on the surface — it does not cut, so panels must be cut accurately before they reach it. Neither machine has a bobbin; both run from cones.

For a rigid woven line the table reads the other way: 301 for construction, 401 for mainseams and flat-felled seams, and a 516 five-thread safety stitch (401 + 504 together) where a woven needs seaming and edge neatening in one pass — jeans and workwear, exactly the territory this site is about.

And if all you have is a lockstitch and a knit to hem: SCHMETZ’s own fallback is a small zigzag, stitch length 1.5–2 mm, width 1 mm, or your machine’s stretch stitch. On a lockstitch, a Stretch twin needle NM 75 at 2.5 or 4.0 mm spacing with water-soluble backing underneath gives a coverstitch-looking hem without tunnelling. These are compromises, not equivalents.

What Thread for Each?

• Knits: fine polyester in the needles — it has the extension to survive the seam stretching — and textured (DTY) polyester in the loopers, which stretches further still and covers the edge. Cotton thread is excluded: it neither stretches with the knit nor tolerates the duty.