Zippers: Types, Sizes and How to Choose the Right One

A zipper is almost always the first thing to fail on a garment, a bag or a soft case — and almost never the thing anyone specified carefully. It gets chosen last, off a colour card, usually by copying the previous season.

This guide explains what the numbers on a zipper actually mean, how the three main chain types behave differently under real load, and why the failure you should be specifying against is usually the slider rather than the chain.

Two tiers of confidence run through this guide, and they are not interchangeable:

• Standard — defined by a published test method (for example ASTM D2061 for zipper strength). Quotable and checkable.
• Convention / Verify required — widely used trade practice with no governing standard, or typical mill values. Treat both as a starting point and confirm against a physical sample.

Every zipper has the same basic parts:

The number stamped on the back of the slider — #3, #4.5, #5, #8, #10 — is described across the trade as approximating the width of the closed chain in millimetres. A #5 chain measures roughly 5 mm across the closed teeth.

Two important caveats:

1. It is a convention, not a standard. No standards body assigns these numbers. The gauge tells you approximately how wide the closed chain is, and nothing else. Two #8 zippers from two mills will be the same width and can be entirely different products in strength, tape and slider quality.
2. The number maps to different widths depending on chain type. The table below gives approximate closed-chain widths in common trade use; expect variation between mills of roughly ±0.5 mm and always measure a physical sample.

Where each gauge typically belongs:

Bigger is not automatically better. A #10 chain on a panel engineered around a #5 changes your seam allowance, your lid geometry and how the closure sits. Match the gauge to the load, not to the aesthetic.

Individual teeth of brass, aluminium or zinc alloy clamped onto heavy tape, often in a Y-shaped profile.

• Strengths: very high linear strength, premium appearance, excellent for straight seams — this is why the classic jeans zipper is metal.
• Weaknesses: heavier, sharp-edged, and point-loaded on curves. Less suited to seams under sustained lateral (horizontal) tension.
• Watch for: plating compliance. Metal components in prolonged skin contact fall under REACH Annex XVII, Entry 27 (nickel release limits) for the EU market.

Discrete teeth injection-moulded directly onto the tape. Weight between metal and coil.

• Strengths: shrugs off grit, mud and frost; takes bright or matched colour well; lighter than metal.
• Weaknesses: stiffer around corners than coil. A single sheared tooth is terminal — the chain cannot be re-formed.
• Typical use: jackets, parkas, ski wear, duffel ends — anywhere weather arrives with dirt.

A continuous spiral of monofilament polyester sewn to the tape.

• Strengths: flexible and very durable under horizontal strain, because the coiled design distributes lateral loads. Ideal for curved seams and fitted garments.
• Weaknesses: the stitch thread holding the spiral to the tape sits exposed on the outer face and can abrade through if dragged repeatedly across rough surfaces — once that happens the coil peels off the tape.
• Variants: reverse coil (spiral on the reverse face, showing a flat tape outward — cleaner look and slightly better weather resistance); invisible / concealed coil, where the tape is folded so only the slider is visible; and a flattened racquet coil profile that recesses the holding thread into a groove for greater abrasion resistance on luggage. Abrasion performance differs between chain profiles in ways worth asking your mill to document if bags or luggage are your market.

This is the single most overlooked decision on the whole hardware list.

If there is any lateral tension across the closure, specify an automatic lock. It is the difference between a closure that stays shut and one that creeps open in wear.

Also decide: one slider or two? Two facing sliders (two-way) allow a long coat to be opened from the bottom for comfort, and let luggage be padlocked. That is a functional decision, not a decorative one.

ASTM D2061, Standard Test Methods for Strength Tests for Zippers, is the reference test method — ten groups of tests in a single document. The standard notes that not every method is suitable for every type of zipper, so you are expected to select the applicable ones:

1. Strength of chains and elements
2. Holding strength of stops
3. Holding strength of separable units
4. Resistance to cushioned compression of sliders
5. Slider deflection and recovery
6. Resistance to twist of pull and slider
7. Torsional resistance of slider pull for removal of components
8. Resistance to pull-off of slider pull
9. Resistance to angular pull-off of slider pull
10. Holding strength of slider lock

Read that list against how a closure actually dies. The chain rarely tears. What fails is the slider, the stop at the end of the run, or the pull coming away in the hand. Six of the ten test groups concern the slider and pull. Which reframes the whole purchase decision: you are not buying a chain, you are buying a slider riding on a chain, and specifying the slider properly matters more than the gauge.

1. Gauge and where it applies — main closure and interior pockets are frequently not the same size.
2. Chain type — coil, moulded plastic or metal tooth.
3. Slider type and lock — non-lock, semi-automatic or automatic.
4. Puller — material, finish, branding, and whether it is replaceable.
5. Tape — width, material and colour. Approve against a physical sample, not a catalogue code, and where quantity allows, order a single dye lot so screening components match shell fabric.
6. Opening type and number of sliders — closed-end, open-end, two-way, X or O.
7. Test methods and acceptance criteria — which parts of ASTM D2061 apply, and the value that passes. Without line 7 the other six are preferences, not a specification.

• Slider jaw spread. Caused by chronic overloading of a too-small gauge. The chain can no longer be gathered; there is no repair, only replacement.
• Abraded coil stitching. Expect it on luggage dragged over concrete and carousels. Specify a flattened racquet-profile coil where this is the use case.
• Forced misalignment. Dragging a slider over a misaligned chain is the fastest way to destroy one. Back the slider off and re-seat the chain gently.
• Salt, sand and frost. Rinsing and drying a coastal or ski closure extends life considerably.
• Washing. Wash zippers closed so elements do not catch on other garments, and avoid prolonged contact with metal chain on wet fabric to reduce staining risk.

• OEKO-TEX® STANDARD 100, Class I for baby and toddler articles.
• REACH Annex XVII, Entry 27 (nickel release) for metal components in prolonged skin contact.
• US CPSIA lead limits for children’s products.

It is the gauge — a trade convention indicating the closed chain measures approximately 5 mm across. It is not a standard and not a strength guarantee. For metal chains #5 typically measures nearer 6.5 mm; always measure a sample.

They resist different things. Metal is strongest in straight-line tension. Nylon coil handles curvature and lateral strain best because the coil distributes horizontal loads. Moulded plastic sits between the two and deals best with grit and icing.

A slider with an internal spring-loaded prong that engages the elements whenever the pull is not being pulled. It prevents the slider creeping open under load — standard for trousers, jeans and bags.

#5 metal closed-end with an automatic-lock slider is the industry default.

Yes, in most cases. You need the gauge, the chain type, the opening type, the slider lock type and the length — measured along the tape from top stop to bottom stop, not along the teeth. If any of those are uncertain, take a photograph and measurements to your supplier.

Almost always a non-lock slider being used where an automatic-lock was needed, or a slider whose jaws have spread from overloading.

Gauges and dimensions in this guide are industry reference values; confirm against a physical sample and your supplier’s specification sheet before ordering.

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