Manufacturer · Fashion & Home Accessories
Trousers and skirts most often use a closed-end YKK coil zip No. 3, and No. 5 for heavier fabrics, always with an auto-lock slider. The lock is key: it stops the fly from sliding down when sitting and moving. The length is set by the style – shorter for a fly, longer for a skirt side seam.
Why a YKK zip for trousers is a separate question
The trouser zip is one of the most stressed points of the garment. It is opened and closed many times every day, takes strain at the waist and is washed with the garment. If the slider doesn't lock reliably or the coil is too fine for the fabric, complaints come quickly. That is why in series production brands often specify YKK – for consistent quality in every batch.
Coil size
| Garment | Recommended size | Note |
|---|---|---|
| Women's trousers in light fabric | No. 3 | Doesn't weigh down the seam or show through the fabric |
| Classic men's trousers | No. 3 or No. 5 | No. 5 for wool and heavier blends |
| Skirt with a side or back seam | No. 3 | Or an invisible zip for fitted styles |
| Work or hiking trousers | No. 5 | For greater load |
| Jeans | Metal zip | See YKK metal zips |
For jeans and heavy denim, a coil zip is usually not the first choice – YKK metal zips are used there, as they withstand the higher load and suit the look.
The slider – the most important part on trousers
Auto-lock
An auto-lock slider has a small pin that engages between the coils when the pull is pushed down. The slider then stays in place until the pull is lifted. This is the standard for flies.
Non-lock slider
It moves freely and is suitable for pockets, decorative zips and products where no load is expected. It is not recommended for a fly.
Pull shape
Trousers use a narrow pull that lies flat under the fly placket and doesn't create a bulge. On skirts with a side zip the pull can be slightly wider for an easy grip. If you want a pull with your logo, that is a separate topic – with YKK the options are confirmed on inquiry.
Zip length for trousers and skirts
Length is measured from the top of the top stops to the bottom of the bottom stop – excluding the tape above and below them. To determine the required length:
- Measure the fly opening or the seam on the pattern, after seam allowances.
- Check whether the top of the zip goes into the waistband or reaches its edge.
- Take the size range into account – with a wide range of sizes, two lengths are sometimes used.
- Make a sample and try it on to check comfort when sitting.
In practice the fly is shortest on a low rise and longer on a high rise; on a skirt, the side or back zip must let the garment pass over the hips without effort.
Zip colour
On trousers the zip is hidden under the placket, but the tape shows when the fly is open and sometimes along the edge of the seam. So the colour must match the fabric. The safest approach is to quote a number from the YKK colour card. If you are torn between two shades, the darker one is usually the safer choice.
Common specification mistakes
- Too fine a zip for heavy fabric – a No. 3 in heavy wool or corduroy can split under strain.
- A non-lock slider on a fly – the zip slides down by itself during wear.
- Unspecified length – "about 18 cm" is not a specification; give the exact measurement.
- Colour from a photo – a screen doesn't show the real shade; use the card or a fabric sample.
- Different zip makes in one order – if part of the batch has YKK and part another zip, the differences in feel and look show.
Invisible or visible zip on a skirt
On fitted skirts and dresses with a smooth line, an invisible zip looks better, leaving only a thin seam line. For these, see the YKK invisible zips line. A classic coil zip with a placket suits sporty and business skirts, where the seam is marked anyway.
Sewing in series production
Once the zip is chosen correctly, what remains is consistent sewing on the line. A few practical tips from garment factories:
- Use a zipper foot and set the distance from the coil so that the slider runs freely without catching the fabric.
- Secure the bottom of the fly with a bar tack just below the bottom stop – that is where the strain is greatest.
- Don't press the coil with the iron during finishing; iron through a cloth at a moderate temperature.
- With every new shell fabric, check that the zip opens and closes smoothly after sewing – some fabrics shrink and make the tape ripple.
- Keep zips from the same delivery for one batch of products so there are no visible shade differences.
These small details often matter more than the choice of brand itself. A good zip sewn in incorrectly can also cause problems.
Ordering YKK zips for trousers through Polkom
Polkom is a Bulgarian manufacturer of accessories for fashion, furniture, footwear and bags, and also offers original YKK zips to garment factories and brands. Browse the YKK coil zips and send an inquiry with the style, fabric, size, length and colour. We will confirm an option, offer a sample and send a quote; minimum quantities depend on the article.
