Most fastener disputes are decided by a sentence the buyer wrote in an enquiry rather than by anything the factory did. "High-strength tie rods, grade 8.8, to EN ISO 898-1" produces an order a factory can quote and a site can build. "Formwork tie rods, good quality" produces an order that is argued about for six months.
This article is about the gap between those two sentences: how to write a formwork fastener specification that survives contact with production, delivery and site assembly.
Start with the function, not the part
The specification has to answer one question first: what does this part do in the structure? A tie rod that carries the lateral load through a wall, a clamp that restrains a beam, and a nut that holds a plate are three different engineering problems, and they fail in three different ways. A grade written for one is wrong for the other two.
Once the function is fixed, five things must be stated numerically. Everything else is preference:
- Grade or material class, against the standard you will certify against.
- Dimensions and tolerances, stated so the assembled product performs as calculated.
- Coating, with mass or thickness and coverage.
- Marking, permanent, with what exactly is on it.
- Acceptance criteria, so both sides know what "conforming" means before the goods ship.
Those five are the specification. Everything beyond them is decoration that usually causes arguments.
Grade: the field most often left vague
Grade causes more disputes than any other field, because "high-strength" is not a number. It means whatever the reader assumes, and on a mixed order the assumption varies from line to line.
For tie rods the common grades are:
| Grade | Typical use | Notes |
|---|---|---|
| 4.8 | Non-structural, positioning | Not for through-ties in walls |
| 8.8 | Standard structural through-ties | The usual default for wall formwork |
| 10.9 | Higher capacity, thinner section | Requires checking the concrete cone, see grade selection |
The critical point is not the grade itself but the failure mode it implies. A higher grade rod does not automatically give a stronger wall: if the concrete cone that anchors the rod governs, raising the steel strength changes nothing. That calculation is in D15 safe working load.
Write the grade numerically, name the standard, and repeat it on the purchase order. An enquiry is a negotiation; a purchase order is a contract.
Tolerances: precision you can pay for
Tight tolerance is not automatically better. Thread precision costs money in tooling, setup and inspection, and it buys nothing if it is finer than the engagement requires.
The governing check for tie rods is the nut-to-thread fit on the assembled product — does the nut run by hand, or does it need a wrench and persuasion, and does it stay tight under load without a washer chewing into the rod. Specify the fit class rather than a pitch diameter tolerance, because the pitch is one variable among several that determine whether the nut seats properly.
For a through-tie on a wall, what matters practically is that the plate sits flat, that the nut bears evenly, and that the rod does not vary enough between units to require rework on site. State the length tolerance and the mass tolerance, and leave thread precision to the fit class.
Coating: the field most often assumed
Coating is frequently written as "galvanized" with no further detail, which is the same as writing nothing. Specify:
- Mass or thickness numerically. For hot-dip galvanizing on non-immersed structural steel, a minimum around 70 g/m² is a common floor.
- What is covered — weld seams, cut edges, thread, holes.
- Whether thread is coated or masked, since a galvanised thread changes nut fit.
- The standard being certified against, and what the acceptance test is.
The thread question matters more than buyers expect. A galvanised or zinc-flake coated thread has a slightly changed dimension, and a nut specified for a bare thread may not seat as intended. Either specify the nut to match, or state that threads are masked and left bare.
Marking: the cheapest insurance in the whole order
Formwork hardware is bought, stored, issued and returned in cycles, and on a rental fleet it cycles through dozens of sites. Permanent marking with the grade and the manufacturer's mark is what lets a batch be traced when a question is asked after the pour.
Marking also does practical work on site. A crew sorting returned hardware needs to know which parts are replaceable consumables and which are reusable structural items. A grade stamp settles that in seconds. Marking cost per part is trivial against the cost of a mixed inventory.
Specify what goes on the mark: grade, manufacturer, batch or heat number, and size where the same grade covers several sizes.
Acceptance: define conforming before the goods ship
The last clause block is the one that prevents most disputes. Both sides should agree, in writing, what conforming means before production starts:
- Dimensional verification by sample: how many pieces, which dimensions.
- Mechanical testing: proof load, tensile test, hardness testing. The method matters — a proof load on a tie rod is a different test from a tensile test on a specimen.
- Coating verification: mass per unit area or thickness, and how many test points.
- Marking verification.
- What happens on failure: rework, replacement, or credit, and who decides.
Where the buyer wants independent confirmation on a large or critical order, specifying third-party inspection in advance is cheaper than arguing about results afterwards. The scope of such an inspection is set out in third-party inspection.
Packaging is a specification item, not a logistics detail
Export packaging changes the delivered condition of the product, so it belongs in the specification rather than in a shipping note. Bare steel parts in an open crate abrade each other in transit and lose coating before they reach site. Boxes, banding, pallet counts and desiccant for coated parts are not extravagances.
The full treatment — including container loading and what customs actually needs on the paperwork — is in shipping tie rods and container loading and export packing and rust prevention.
What to check before issuing the purchase order
- Is every grade stated numerically against a named standard, on the purchase order and not only in the enquiry?
- Are dimensions and the nut-to-thread fit class both stated?
- Is coating given as mass or thickness, with coverage and thread treatment specified?
- Is permanent marking specified, with exactly what goes on the mark?
- Are acceptance criteria and the failure procedure agreed in writing?
- Is packaging specified as part of the order?
If any answer is "not stated", the cheapest moment to fix it is now, in the order document, rather than later in a claim.