Headrail in Finished venetian blinds: Range, Tolerance and How to Test It

Buyers argue about headrail more than about any other figure in finished blinds, and they usually argue about the wrong part of it: the number itself rather than the tolerance behind it.

What headrail actually controls in finished blinds

Steel is stronger and rusts; aluminium is lighter and costs more.

This is why two suppliers can quote the same headline price and deliver products that behave differently in the second year.

For Finished venetian blinds, the working range is 25 mm steel or aluminium. Inside that band the choice is commercial; outside it, the product changes category and so does the price.

What 25 mm steel or aluminium does not tell you

Specifying the ceiling is only justified when the end product carries a warranty that would be expensive to honour. Otherwise it is cost without a customer-visible benefit.

The figure that decides the outcome is not headrail itself but the tolerance around it. A supplier who quotes 25 mm steel or aluminium without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.

How to measure headrail

The reference method here is Operation cycles, run to internal 5000 cycles, with an acceptance of no slip, no fray. The method is the easy part; sampling and conditioning are where reports diverge.

Measure on the goods as delivered, not on the greige or the pre-finished material. The figure that matters is the one in the product your customer receives.

Record the measured value rather than pass or fail. A marginal pass on headrail tells you the process is running at the edge, which is the information you need before the next lot rather than after it.

Headrail does not stand alone

Headrail moves with slat (25 / 35 / 50 mm, wood or PVC) and with ladder tape / cord (polyester, 12-25 mm). Tightening one usually costs money in another, and a supplier who accepts every tolerance without comment has either not understood the interaction or is planning to substitute.

This is why a specification written as a list of independent tolerances is weaker than one written as a construction. The list lets a supplier satisfy each line while missing the product.

The clause to write for headrail

The line below is the version we can quote against without inventing anything. Headrail appears with a tolerance and a test, not as a standalone number.

50 mm basswood venetian blind, 25 mm steel headrail, branded cord lock, 5000-cycle tested, cordless with tension device to EN 13120, square within 2 mm, stain 3A, valance included

Write it once and reuse it. The buyers who avoid claims are not stricter than everyone else; they send the same well-written clause every time.

When headrail goes wrong

Cord lock slipping. The blind creeps down and will not hold position.

The cause is usually cheap zinc die-cast lock or a cord that is out of specification for diameter.

The test that catches it: Cycle test 5000 up/down operations with a 5 kg load.

What to specify instead: Specify a branded lock, matched cord, and cycle-test the assembled blind rather than the component.

None of this is visible in a quotation. It becomes visible in a retained sample and a lot record, which is why the paperwork matters more than the price on this parameter.

Four questions about headrail, before you order

1. What tolerance do you hold on headrail, and what did your last three lots measure against it?
2. Which method do you use for operation cycles, and which laboratory signs the report?
3. When headrail falls outside 25 mm steel or aluminium, do you rework, downgrade, or ship and hope?
4. Which of slat or ladder tape / cord would you move first to hit a lower price?

The answers are more useful than a certificate, because they show whether the process is controlled or merely inspected. Full ranges for finished blinds are on the product page, and the measurement regime is described on the quality control page.

Seven lines that turn a quotation into a specification

Most post-delivery arguments are not about quality. They are about a document that never said which figure would be measured, on which instrument, at whose cost.

1. Cord lock (standard / auto-lock / cordless): state where in the band this order sits. The middle of the band is not what a tolerance is for.
2. Bottom rail: the figure you will accept inside the wood, PVC, or aluminium band, the tolerance on it, and the method used to measure it.
3. Child safety (cordless / tension device / short cord): name the number, not the word. If the answer only repeats the band, ask which point inside it is being offered for this order.
4. Width tolerance: 1-2 mm on the finished blind is the market band. Fix the figure you will test at goods-in, and the instrument you will test it with.
5. Price validity: the period during which the quoted figure holds, and what happens to it when the raw-material index moves.
6. Remedy: rework, replacement or credit, and the point at which each applies.
7. Sample retention: one production sample per lot stays with the mill for twelve months. Claims are settled against it, not against memory.

Three questions, and the answers that separate mills

If the finished blinds figures on this page is going to be decided on a call, take these three questions into it.

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