Trim Pull-Test and Salt Spray Requirements: A Buyer's Reference Table
Pull strength in newtons and salt spray hours by trim type, the test methods behind the numbers, and how to write both into a tech pack and an RFQ without over-specifying.
Two numbers settle most trim claims: how hard a component resists being pulled off, and how many hours its plating survives neutral salt spray. The tables below give the thresholds buyers normally write into a tech pack, the methods behind them, and how to specify both without over- or under-buying.
Why these two tests, and not twenty
In twenty-eight years of making buttons, snaps and hardware, the claims that reach a chargeback almost always land on one of two failures. The part separates from the garment, or the finish goes dull, spotted or rusty before the wash cycle is over. Tensile strength covers the first. Salt spray covers the second. Fit, colour and hand-feel matter, but they are argued at approval, not after shipment.
Everything else in a trim spec exists to protect these two outcomes. If your tech pack fixes pull strength and plating endurance, the rest of the specification has something to hang on. Those two numbers are also the two a vendor cannot argue with at quotation stage — either the part meets them or it does not.
The failure modes behind each number are worth reading before you write the spec: why snap fasteners fail the pull test and why tack buttons break on denim.
Pull and attachment strength by component
| Component | Typical use | Attachment requirement | Method |
|---|---|---|---|
| Prong snap (ring snap) | Baby and kids' wear | 90 N minimum, no separation | 16 CFR 1500.51 tension; brand spec often stricter |
| Prong snap (ring snap) | Adult shirts, jackets | 60–80 N | Same method, adult threshold |
| Tack button (jean button) | Denim, workwear, bags | 150–250 N on the shank | Pull perpendicular to shank, 20 mm/min |
| Sew-through button | Shirting, blouses, knit tops | 50–70 N (5–7 kgf) | Two-thread attachment, pull to failure |
| Shank button | Coats, tailored jackets | 60–80 N | Pull on shank, not the face |
| Rivet | Denim pockets, workwear stress points | 120–180 N | Clamp and pull along rivet axis |
| Eyelet / grommet | Lacing, drawcords, bags | 100–150 N | Pull perpendicular to setting |
| Zipper slider and puller | All zipped goods | 50–70 N | ASTM D2061 strength tests |
| D-ring, buckle, hook | Bags, straps, outerwear | 200–300 N | Loaded through the bar, not the frame |
| Cord lock | Drawcords, hoods, bags | 80–120 N | Cord clamped, pull to slip or break |
These are typical brand requirements, not legal limits. Children's items under three years also fall under the small-parts rule at 16 CFR 1501, which applies to the component itself as well as the attachment. If your buyer's manual names a different number, the buyer's number wins — quote against theirs and state the test method, so both sides are measuring the same thing.
Salt spray hours by finish
Salt spray is run to ASTM B117: continuous fog, 35 °C, 5% sodium chloride, parts at 20° from vertical. The clock stops when white corrosion covers more than 5% of the visible surface, or when red rust appears, whichever the buyer defines first. Write that definition into the spec, otherwise two labs will report different hours for the same part.
| Finish | White corrosion | Red rust | Where it is used |
|---|---|---|---|
| Bright nickel, 0.1 µm | 24 h | 48 h | General apparel buttons |
| Bright nickel, 0.25 µm | 48 h | 96 h | Outerwear, workwear |
| Nickel-free (palladium or tin) | 48 h | 72 h | Kids' wear, nickel-sensitive markets |
| Antique brass, lacquered | 24–48 h | Not applicable | Denim, bags, vintage finishes |
| Gunmetal, electrophoretic coat | 48–72 h | 96 h | Bags, outerwear hardware |
| Anodized aluminium | 72 h | Not applicable | Lightweight trims, colour anodizing |
| Powder-coated zinc alloy | 48 h | 96 h | Bag hardware, buckles |
Hours are a qualification threshold, not a service-life prediction. A 48-hour part is not "twice as good" as a 24-hour part; it clears a different bar. Plating thickness, not the base metal, is what decides which bar a part clears — a thicker deposit on the same zinc alloy body moves a part from the 24-hour row to the 48-hour row, and that change is a plating-line decision, not a design decision.
How to run the test so the result means something
- Sample five pieces per component per lot, drawn from at least two cartons.
- Condition samples 24 hours at 23 °C and 50% relative humidity before testing.
- Pull at 20 mm/min on a calibrated tensile stand, and record the failure mode: shank pull-out, prong deformation, fabric tear, or button fracture. The mode tells you who owns the problem.
- For salt spray, photograph the same three parts at 24, 48 and 72 hours under daylight lamps. Photos settle arguments faster than a report.
- Keep results against the production batch number. Without the batch number, a test result cannot be tied to the goods in your warehouse.
That last point is the one buyers forget to ask for. A test report with no batch number is a report about somebody's sample, not about your shipment.
Wording that survives an argument
A spec that says "good quality snaps" gives a factory nothing to hit and a QC team nothing to reject. Put numbers and a failure definition in the tech pack, and repeat them in the RFQ so the quotation is priced against the same requirement:
> Prong snap, 15 mm cap, nickel-free finish. Attachment strength 90 N minimum when pulled perpendicular to the cap at 20 mm/min, tested on 5 pcs per lot after 24 h conditioning. No separation of cap, socket, or post from the shell fabric. Salt spray ASTM B117, 48 h, no white corrosion above 5% of visible surface.
That paragraph costs four lines and prevents most of the arguments that start six weeks later, when the goods are already on water.
How to put these numbers in the RFQ
An RFQ that lists only style, quantity and target price gets a price for a generic part. Add four lines and the quotation becomes comparable:
- Test requirement per item — pull strength in newtons, salt spray hours, and which method (16 CFR 1500.51, ASTM B117, ASTM D2061).
- Acceptance rule — what counts as a failure, and whether AQL inspection at pre-shipment uses the same definition.
- Report requirement — per-lot in-house report tied to the batch number, or a third-party report from a named laboratory.
- Who signs the approval sample — the sample that becomes the bulk reference, and where it is kept.
The mistake we see most
Buyers copy a pull number from a different category. A 90 N requirement written for a baby bodysuit snap gets pasted onto an adult parka, and suddenly a perfectly good 70 N snap reads as a failure. The number is not a quality score. It is a threshold matched to the risk of the end use: a component a child can mouth needs more resistance than a decorative button on a coat.
Match the threshold to the wearer and the wash cycle, not to the last spec you approved.
FAQ
Send the tech pack with the pull strength, salt spray hours and the batch-report requirement, and we will quote against those numbers and send the test record with the first counter sample.
Senfa Mfg Email: [email protected]
Last updated: 2026-11-06