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Road transport has very specific requirements for the grommets that reinforce the tarpaulins of semi-trailers. A TIR grommet is not simply a larger metal ring: it must meet standardised dimensions that guarantee compatibility with the tensioning systems used throughout the European logistics chain, from trailer builder to terminal operator.
At Industria Acosta Pramon we have been manufacturing TIR grommets in brass for decades, in both standard sizes: 40×10 and 40×20. This guide explains what the TIR standard requires, how to carry out a full installation, and when to use each size.
What the TIR standard requires from the grommet
TIR stands for Transports Internationaux Routiers, the international customs convention governing sealed-load road transport. One of its physical requirements is that the tarpaulins of TIR vehicles must be seal-fastened by cables or cords passing through perimeter fastening holes. These holes must be reinforced with grommets of standardised dimensions so that the sealing systems of every customs authority remain compatible.
The TIR grommet specification sets:
- Outer flange diameter: 40 mm (the figure that defines the “40×10” and “40×20” names)
- Minimum pull-out strength: sufficient to withstand the tension of the sealing cable
- Material: brass (the standard specification) or steel with corrosion-resistant finish
- Mandatory installation with a reinforcement washer on the reverse of the tarpaulin
The number after the “×” (10 or 20) indicates the barrel height of the grommet in mm, which determines the material thickness it can pass through.
Technical specifications: 40×10 and 40×20
We manufacture the two standard sizes of TIR grommets in natural brass:
| Reference | Outer diameter | Inner diameter | Barrel height | Recommended tarpaulin thickness | Material |
|---|---|---|---|---|---|
| TIR grommet 40×10 | 40 mm | 20 mm | 10 mm | Up to 6 mm | Brass |
| TIR grommet 40×20 | 40 mm | 20 mm | 20 mm | 6–16 mm | Brass |
The 40×10 is the standard for single-ply tarpaulins or with a perimeter reinforcement tape of up to 5–6 mm total thickness. The 40×20 is used where the tarpaulin has a thicker edge reinforcement, such as tarpaulins with an internal continuous cord or double-sewn edges.
Full TIR installation: grommet + reinforcement washer
Correct installation of a TIR grommet always requires two pieces: the grommet on the outer face of the tarpaulin and the TIR reinforcement washer on the reverse. This pairing is not optional: it is a technical requirement of the TIR system and of every serious trailer manufacturer.
Why is the washer mandatory?
- Truck tarpaulins work under tensile loads far higher than an advertising banner. Without a washer, the grommet can rotate under load and progressively tear the fabric.
- The washer spreads the fastening force over a larger surface, reducing point pressure at the edge of the hole.
- Under constant road vibration, a crimped grommet + washer assembly is the only configuration that guarantees the piece will not loosen in use.
Our reinforcement washers specifically for TIR installation:
| Reference | Pairs with grommet | Material |
|---|---|---|
| TIR washer 40×10 | TIR grommet 40×10 | Brass |
| TIR washer 40×20 | TIR grommet 40×20 | Brass |
Sourcing both grommet and washer from the same manufacturer guarantees dimensional compatibility and a uniform crimped finish.
Applications for trailer builders and logistics operators
Truck and trailer tarpaulin manufacturers
Companies that build or repair semi-trailer tarpaulins are the main market for the TIR grommet. A standard 13.6 m semi-trailer tarpaulin carries 80 to 120 grommets around its perimeter. Volume per trailer builder is high and reliability is critical: a failed grommet means a roadside tarpaulin repair, with its associated operating cost.
Trailer builders and repairers
Curtainsider trailer builders use TIR grommets both on the top cover tarpaulin and on the sliding side curtains. The side curtain carries grommets along the lower edge for the tensioning-bar system.
Fleet maintenance operators
Transport companies with their own fleet replace damaged or missing TIR grommets as part of preventive tarpaulin maintenance. A quarterly order of 500–2,000 units is typical for mid-sized fleets.
Industrial marquee and storage manufacturers
PVC storage marquees, temporary agricultural hangars and demountable industrial halls use TIR grommets on perimeter edges for their higher strength compared to standard grommets.
Certification and manufacturing quality
Acosta TIR grommets are manufactured in brass at our Barcelona plant. Brass provides:
- Corrosion resistance without additional coating
- Appropriate ductility for clean barrel forming during crimping, without cracking
- Compatibility with the standard setting presses used in the trailer-building sector
- Uniform appearance across production, without batch-to-batch variation
See the full TIR grommet catalogue for all available references.
FAQ — TIR grommets
What is the difference between a 40×10 and a 40×20 grommet?
The difference is the barrel height: 10 mm for the first, 20 mm for the second. The 40×10 is for single-ply tarpaulins of up to 6 mm total thickness; the 40×20 for tarpaulins with a thicker edge reinforcement (6–16 mm). Both share the same 40 mm outer diameter and 20 mm inner diameter.
Can I use a TIR grommet without a washer?
Technically it can be fitted, but it is not correct practice. Without a washer the grommet can rotate under tensile load, progressively abrading the hole in the tarpaulin until pull-out occurs. On certified TIR installations the washer is mandatory.
Which machine sets 40×10 and 40×20 TIR grommets?
Because of their size (40 mm outer diameter), TIR grommets require a bench press or a pneumatic machine with the correct die for that diameter. They cannot be installed properly with standard manual pliers. See our grommet setting machines.
Do you manufacture TIR grommets in materials other than brass?
Brass is the standard TIR grommet material for its excellent balance of price, mechanical strength and corrosion resistance. For specific applications that require stainless steel (e.g. refrigerated bodies washed with disinfectants) please contact us for bespoke production.
Request a quote for TIR grommets
We supply TIR grommets to trailer builders, tarpaulin workshops and fleet managers across Spain and Europe. Volume pricing, 24–48 h lead time on stock references and technical advice for any application question.
Installation guide: setting a TIR grommet correctly
Installing TIR grommets requires tools appropriate for the piece size. The correct process is:
- Prepare the edge of the tarpaulin. A truck tarpaulin typically has an internal continuous cord or a heat-welded reinforcement profile along its edge. The TIR grommet must pass through the full thickness of that reinforcement. Check that the grommet barrel (10 mm or 20 mm depending on the reference) is long enough for the total edge thickness.
- Punch with the correct hole punch. The hole diameter must match the inner diameter of the grommet barrel (20 mm). A larger hole leaves the grommet loose; smaller, and the barrel will not enter cleanly.
- Insert the TIR grommet from the outer face of the tarpaulin. The flange stays visible on the outer face (the face seen from outside the vehicle).
- Place the reinforcement washer on the reverse. The TIR washer (reference 40×10 or 40×20 depending on the grommet) goes inside the trailer, pressed against the edge reinforcement.
- Crimp with a bench press or pneumatic machine. Because of the TIR grommet flange size (40 mm), manual pliers are not sufficient. A robust bench press is the minimum; for series production, a pneumatic press.
- Check the crimp. The grommet must not rotate or have axial play. The washer should sit perfectly flat against the tarpaulin with no wrinkles in the surrounding material.
Common technical questions from trailer builders and tarpaulin workshops
We regularly receive technical questions from trailer builders and tarpaulin repair workshops. These are the most common:
What is the correct spacing between TIR grommets on a semi-trailer tarpaulin?
The TIR standard sets a maximum spacing between seal holes. In practice most semi-trailer tarpaulin manufacturers install TIR grommets every 200–250 mm around the perimeter. This spacing ensures the sealing cable cannot access the interior without tearing the tarpaulin or breaking the seal.
Can damaged TIR grommets be repaired in the field?
Yes, but a TIR grommet torn out in transit is an emergency repair that must be completed properly at the next available workshop. A failed TIR grommet means the seal cannot be fitted at that point, which can be a problem at customs checks. We recommend transporters always carry a small stock of spare TIR grommets and washers for roadside replacement.