GRP rod is a solid pultruded round bar: glass fibre drawn straight through a heated die with resin and cured, with no hollow in the middle. NA-ME makes it in 19 standard diameters from Ø4 mm to Ø55 mm. It is the section you reach for when the part has to be small, stiff, strong along its length and electrically non-conductive — pins, dowels, tie bars, spacers, grating connectors. This page explains where a solid bar behaves differently from a tube, how the codes are read, and which resin belongs in which environment.
A hollow tube is the efficient way to buy bending stiffness, because it puts the material where the stress is and leaves the middle empty. That is the right trade when the part is long and its job is to span or to stand. It is the wrong trade when the part is short.
A rod is chosen for the opposite set of reasons. It has full material at the centre, so it takes bearing, shear and compression across the whole section rather than through a thin wall. That is what a pin does: it sits in a hole and is loaded across its diameter. A tube in the same place would crush. A rod can be turned, threaded, cross-drilled or machined at the end without leaving a hollow to seal, and at small diameters — Ø4 to Ø12 mm — a hollow section is not practically manufacturable anyway.
The other half of the argument is tension. Pultrusion aligns the glass along the pull, so a solid bar loaded along its length is working the fibres in the direction they are strongest. That is why a rod makes a good tie or stay and a poor cantilever: pull it and it performs, load it sideways and you are back to the low modulus that governs every GRP section.
You will see the same product written as FRP rod, fiberglass rod, pultruded round bar or GFK rod depending on where the specification was drafted. For a glass-fibre profile they all mean this section.
| Code | Diameter Ø (mm) | Weight (kg/m) |
|---|---|---|
| CPR-O-101 | 4 | 0.02 |
| CPR-O-102 | 6 | 0.06 |
| CPR-O-103 | 8 | 0.10 |
| CPR-O-104 | 10 | 0.16 |
| CPR-O-105 | 12 | 0.23 |
| CPR-O-106 | 15 | 0.36 |
| CPR-O-107 | 16 | 0.41 |
| CPR-O-108 | 18 | 0.49 |
| CPR-O-109 | 20 | 0.62 |
| CPR-O-110 | 25 | 0.97 |
| CPR-O-111 | 27 | 1.06 |
| CPR-O-112 | 30 | 1.34 |
| CPR-O-113 | 32 | 1.44 |
| CPR-O-114 | 33 | 1.48 |
| CPR-O-115 | 40 | 2.25 |
| CPR-O-116 | 42 | 2.60 |
| CPR-O-117 | 45 | 2.79 |
| CPR-O-118 | 48 | 2.97 |
| CPR-O-119 | 55 | 4.85 |
Weights are per metre for the orthophthalic grade. The section number is tied to the diameter, not to the resin, so a CPR-V-109 is the same Ø20 mm bar at the same 0.62 kg/m as a CPR-O-109.
Nineteen diameters cover most work, but NA-ME cuts its own dies, so an intermediate diameter is a matter of quantity and lead time rather than a refusal. Send the diameter you need.
Every profile we make carries a three-part code. Take CPR-O-115:
So the diameter and the resin are two separate decisions, and quoting the number plus the resin letter is enough to describe the product exactly.
The glass carries the load; the resin decides how long the bar survives what surrounds it. Six systems are in production.
These are distinct product codes rather than a finish applied afterwards, which is why the resin has to be settled at order time. The comparison in full is on resin systems; for outdoor exposure, the surface veil that protects the resin from UV is covered on surface veil, UV and fire.
Pinned joints between composite members where a steel pin would corrode or bridge two parts electrically. The bar takes the bearing across its full section.
Short lengths used to locate, lock and tie grating panels together and to their supports, in the same material as the grating so there is nothing to rust at the fixing point.
Members that carry pure tension between two fixed points, where the rod is loaded along its length and the environment would attack a steel tie.
Substations, solar sites, testing rigs and transformer areas: anywhere two conductive parts must be held apart by something that carries load but not current.
Two further uses come up often enough to name. The first is as a tie or stay loaded purely in tension, which is the load case pultrusion is best at. The second is as machining stock: bushes, rollers, guide pins, handles and small turned parts made from a bar that has no metal in it at all. The larger diameters — Ø40 to Ø55 mm — are usually bought for this rather than for structural work.
GRP does not rust, rot or attract insects. It is electrically non-conductive, its thermal conductivity is low, and it stands up to UV, weather and chemical attack. It weighs roughly a quarter of what steel does — a Ø20 mm bar is 0.62 kg/m — and it is lighter than aluminium as well.
The limits are just as important. It is a directional material: strong along the pull, weak across it, so a rod is far better in tension and bearing than in transverse bending. Its modulus of elasticity is low to medium, which is why on almost every span it is deflection rather than strength that decides the section. And it does not weld — every connection is mechanical or bonded, which changes how a job is sequenced. The numbers for a calculation are on mechanical properties; the fixing detail is on installation and fastening; how the section is drawn and cured, and why that makes it repeatable metre after metre, is on the pultrusion process.
NA-ME holds ISO 9001, ISO 14001 and ISO 45001 certification covering the design and manufacture of composite products. The standards above are explained because they appear in buyers’ specifications; we do not present them as certifications we hold. What we test in house, and what we do not, is set out on quality, standards and testing.
If the part is long and its job is to span or to stand, buy the hollow version instead: GRP round tube gives far more bending stiffness per kilogram. For plates, straps and edge trim, see GRP flat bar. Posts and frames are usually FRP square tube. The full family is listed on GRP and FRP structural shapes, and if the material itself is new to you, what is a GRP profile covers the ground in a few minutes.
Tell us the diameter, the length, the quantity and what the rod has to do — pin, tie, spacer, machining stock — plus a sentence on the environment. That is enough to confirm a diameter from the table or to tell you what a new die involves. We have pultruded in Ankara since 1982, around half of what we make is exported, and an EU destination is 3 to 7 days from the plant by road, with no customs duty on industrial goods under the EU–Turkey Customs Union. Small and mixed orders are welcome.