Which twin needle fits my machine? Start from your widest stitch

SCHMETZ says a machine for twin needles should have a zigzag function with a transversal hook, and both needles have to pass through the needle plate and the presser foot. SCHMETZ's US site says twin needles are not for sergers or industrial machines. The spacing is the first number on the pack, in millimeters. Treat the widest stitch your machine sews as the most that spacing can be, follow any limits your manual sets, and turn the first stitches by hand.

• Serger, also called an overlocker, or an industrial machine: don't buy a twin needle.
• Straight stitch only, with no zigzag setting at all: don't buy one. SCHMETZ lists its twins only for machines that sew zigzag.
• Zigzag, but no stitch-width dial: SCHMETZ's condition is a zigzag machine, not a dial. The Janome HD1000 is one such machine. Its instruction book shows a stitch length dial and a pattern selector but no width dial, with zigzag as pattern C. Measure its zigzag as described below.
• Manual says to use only the twin needle supplied with the machine: replace that needle instead of choosing a spacing. The Janome Skyline S6 manual says this.
• Anything else: choose a spacing no wider than your widest stitch, then turn the first stitches by hand. The Singer HD 4552 manual gives 0–6 mm, so an 8.0 is past that ceiling. Singer names no twin size for it, and a 6.0 would sit exactly at the ceiling.

SCHMETZ's US site, run by its North American importer, explains the label this way: on 2.5/75, the first number is the distance between the two needles and the second is the needle size. So 4.0/100 is two size 100 needles 4 mm apart. The importer's pocket guide gives the spacing in millimeters. The twins use the household 130/705 H system, and ZWI on the pack marks a twin: the Stretch Twin reads 130/705 H-S ZWI. If your machine takes another needle system, start with how to read your needle system and size.

SCHMETZ's own site lists the 6.0 and 8.0 as the Extra Wide Universal Twin. The US site sells them as Universal Twin options. For either, SCHMETZ names the straight stitch as the stitch to use. The Topstitch Twin is listed on the US site but not on SCHMETZ's own twin and triple page.

SCHMETZ's rule is that the needle plate and presser foot need an opening large enough for the needle distance and the stitch width you select. None of the five manuals below gives the width of that opening. What you can find is the widest stitch your machine sews, and it works as an upper limit.

A zigzag plate's slot has to let a single needle come down at both edges of the widest stitch. A twin needle sewing a straight stitch in the center position puts one needle half the spacing to each side of center. At a spacing equal to your widest stitch, both needles land where a single needle lands at full width. Any wider, and they come down outside anywhere the machine was built to drop a needle. That makes the widest stitch a ceiling, not a promise of fit, so the hand-turn check below still matters.

On the Singer HD 4552, a 6.0 would sit exactly at that ceiling. SCHMETZ's condition for its 6.0 is a needle plate and foot opening at least 6 mm wide, and the HD 4552 manual doesn't give either width, so the hand-turn check is what settles it.

Look for your widest stitch in the manual's stitch-width section or specification table, and check that it is in millimeters. The Singer HD 4552 manual says its dial numbers are millimeters. The Designer Topaz 65 shows stitch width on its screen in millimeters or inches and sounds a warning when you try to go past the maximum. The Janome 2222 dial runs 0 to 5, but its manual never calls those numbers millimeters, so don't read them as a measurement. The Janome HD1000 has no width dial to read.

No manual? Janome lists its instruction books by model, and Singer's manual page covers Singer, Pfaff and Husqvarna Viking models. Failing that, sew the plain zigzag at its widest setting on scrap. Measure from the center of the thread at one edge to the center of the thread at the other. Measuring from outer edge to outer edge adds the thread's thickness and reads wide. Treat the result as approximate.

Zigzag and decorative stitches need room too. SCHMETZ's rule counts the spacing and the stitch width together. On a 6 mm machine with a 4.0 twin and the needle centered, 6 minus 4 works out to a zigzag no wider than 2 mm. SCHMETZ suggests switching on twin mode, if your machine has one, to limit the stitch width.

The Skyline S6 shows why the manual comes first. Its straight-stitch needle position runs from 0.0 to 9.0, which looks like room for a wide twin. Janome still says to use only the twin needle included with the machine, because another may hit the needle plate, foot or hook and break. Its twin needle key limits the stitch width to 3.0 mm and the straight-stitch needle position to between 3.0 and 6.0. The twin comes in the S6's needle set, part no. 859856005, along with four single needles, and the manual gives the twin no number of its own. If yours is lost, give a Janome dealer your model and ask for the S6 twin needle, or for that set.

On the Designer Topaz 65 you select the twin needle size in the settings, and the machine limits width and position to suit. If stitches later come out narrow, the manual's fix is to switch that setting off.

SCHMETZ's condition also names the hook, and the simplest check is your manual. A twin-needle section shows the maker expects twin needles on that machine, so follow that section and any limits it sets. If the manual is silent, as the Janome 2222's and HD1000's are, turn a few stitches by hand on scrap. Check that both needles clear the plate and the foot, and that both rows of stitches form.

1. Switch the machine off before you change the needle. The Singer, Janome and Husqvarna Viking manuals all say so.
2. Fit the zigzag needle plate, the one with the long slot, and a zigzag foot with a wide opening, not a straight stitch foot. The S6 calls for foot A or F; the HD 4552's all-purpose foot has a wide slot. For other feet, see will this presser foot fit.
3. Set up a second spool, since each needle takes its own thread. The Topaz 65 manual puts it on the auxiliary spool pin, and the S6 manual on the extra spool pin. The HD 4552 has an auxiliary spool pin too, but its manual doesn't cover twin-needle threading.
4. Take both threads through the guides together, as if they were one, then separate them and thread one through each needle eye by hand. That is SCHMETZ's method. If your manual has its own twin-needle threading steps, follow those: the Topaz 65's put one thread on each side of the tension discs.
5. Skip the automatic needle threader. SCHMETZ, Singer, Janome and Husqvarna Viking all say it won't work with twin needles.
6. Center the needle and turn on twin mode if your machine has one. The HD 4552 manual says to set the needle position to center. Raise the needle before you change the stitch width or the stitch: the HD 4552 and 2222 manuals say so for the width dial, and the HD1000's for its pattern selector.
7. Turn the handwheel toward you through the first stitches before you touch the foot control, as SCHMETZ's US site suggests. Both needles should go into the slot without touching the plate or the foot. The S6 manual also says to test twin-needle stitches before you sew on the garment.
8. If the seam arches between the rows, loosen the needle thread tension. SCHMETZ says it usually has to be loosened.

• Asymmetrical twin needles: the Topaz 65 manual says not to use them, because they can damage the machine. Its drawing shows one needle on the full shank and the second fixed beside it on a shorter one.
• Special stitches: in twin mode the S6 won't select buttonholes, darning, eyelets or monograms.
• Leather: SCHMETZ doesn't make a leather twin needle.
• Triple needles: SCHMETZ gives them the same plate-and-foot condition, and a triple takes three needle threads. The Topaz 65's needle threader can't be used with triples either. Turn one through by hand before you sew.
• Industrial machines: SCHMETZ's US site says twin needles aren't for them. If your machine's plate names an industrial system, start with the industrial needle cross-reference.

Singer Heavy Duty owners: the machine's needles, bobbins and feet are covered in what a Singer Heavy Duty takes.