Published by pultrx, the export trading company of Henan Zhongsheng. This is a buyer planning guide; the manufacturer confirms project specifications in writing.
Sizes, bores and weights for every tube, rod and shape mentioned here are in the FRP size chart in inches
Ways to join fiberglass tubes and rods
Most tube joints start the same way: one tube, or a solid rod, slides into the bore of the next size up. What holds the joint is a choice between a removable clamp or pin and a permanent bond. The strongest and most reliable connection between pultruded parts is fitted bolts combined with adhesive on prepared surfaces, according to the Strongwell manual.
| Method | How it is done | Removable | Use it for | Watch for |
|---|---|---|---|---|
| Slot and hose clamp | Saw a short lengthwise slot centered in the end of the outer tube, slide the inner tube in, and close the slotted end with a stainless hose clamp. A second clamp adds grip. | Yes | Telescoping poles, masts and handles that are adjusted or taken apart | Use all-stainless clamps outdoors. The slot weakens the tube end; keep it short and seal the cut. |
| Through pin or bolt | Assemble the joint at its final overlap, drill straight through both tubes on the centerline in one pass, and fit a stainless machine screw or clevis pin. | Yes | Spreaders, frames and joints that must carry load but come apart | Drill the assembled pair so the holes line up. Add thread locker or a bonded nut; use washers to spread the load. |
| Adhesive sleeve | Prepare both surfaces, spread adhesive inside the outer tube and on the inner part, slide together and hold straight while it cures. | No | Permanent extensions, end plugs, stiffening a tube with a rod inside | A rigid epoxy joint does not like repeated bending. Support the assembly straight; it cures in whatever shape it is left. |
| Bonded and bolted | Adhesive on prepared faces plus fitted bolts, screws or rivets that hold the parts while the adhesive cures. | No | Structural frames, brackets and gussets | No waiting for cure before handling; this is the highest-reliability connection. |
| Rivets | Blind or drive rivets through drilled holes, with backup washers. | No | Sheet, angle and channel assemblies, covers | Drill one size over the rivet: a No. 30 drill for a 1/8 in rivet. |
| Threaded inserts | Metal inserts, rivet nuts or helical inserts installed and preferably bonded into the fiberglass; the bolt threads into the metal. | Yes | Removable covers and fittings | Do not rely on threads cut in the fiberglass itself; they wear quickly and hold little. |
| Molded or machined fittings | End caps, ferrules, couplers and tees made to the tube size and bonded or pinned on. | Depends | Repeated assemblies and kits | Order the fitting and tube as a matched pair so the clearance is controlled. |
Nailing works into wood but never fiberglass to fiberglass. Lag screws do not bite well. Self-tapping screws are acceptable for light duty, and better as clamps that hold a bonded joint while it cures. In corrosive service use stainless steel or Monel fasteners, or coat exposed heads.
How to cut fiberglass tube, rod and profiles
Support the part rigidly on both sides of the cut and along its length, so that neither end drops as the blade comes through. Unsupported fiberglass chips and splinters at the exit side of the cut. A wrap of masking tape at the cut line reduces splintering and gives you a surface to mark on; mark which side of the line the waste is, because the kerf removes material.
| Job | Tool | Notes |
|---|---|---|
| A few pieces of rod, bar or small tube | Hacksaw, 24 to 32 teeth per inch, or a grit-edge hacksaw blade | Light, steady strokes. A carpenter's saw works but dulls quickly. |
| Straight cuts in tube and structural shapes | Circular saw, table or radial (miter) saw with a carbide or diamond grit-edge blade | A table or miter saw cuts squarer than a hand saw. Toothed carbide-tipped blades are not recommended: they vibrate and throw teeth. |
| Production cutting | Diamond blade, 60 to 80 grit | Water cooling gives faster, smoother cuts and less dust; plan for the wastewater. |
| Large sections | Two passes with a circular saw (half from each side), or a power band saw with a grit-edge blade and automatic feed | Roll a tube through the band saw for a smoother cut. |
| Curves, circles and cut-outs | Saber saw or band saw; router with a carbide or diamond bit | A router removes more stock than a saw. |
- Use light, even pressure. Forcing the blade clogs it with dust, heats the cut and shortens blade life.
- If the cut edge frays or turns black, the resin is overheating: slow the cutting speed.
- A clogged grit-edge or diamond blade can be cleared by cutting a common brick.
- Shearing is a fast but rough method and needs a specially shaped blade; do not shear material over 3/16 in thick.
- Long lengths flex and twist while being machined. Support them along their length, not only at the cut.
Drilling fiberglass
High speed steel drills cut fiberglass but dull quickly; use carbide-tipped drills for any quantity of holes. Run at roughly the speed you would use for hardwood and let the drill cut without heavy feed pressure. Pushing hard punches through the far side and splinters the surface fibers around the exit. A wood backup block behind the part, or masking tape over the hole position, reduces break-out.
- Holes in pultruded profiles come out about 0.002 to 0.004 in undersize, because the material springs back. For close fits drill one size up: a 1/8 in drill will not pass a 1/8 in rivet, a No. 30 drill will.
- In a hollow tube, drill the first wall, then ease off as the drill reaches the far wall so the exit hole does not tear.
- For a pinned joint, drill the assembled tubes in one pass so the holes in both stay in line.
- Punching is possible in thin material with sharp, specially shaped punches and a stripper; oversize punched holes by 0.020 to 0.030 in and expect to re-drill holes that must be accurate.
Seal every cut end and hole
Pultruded profiles carry a resin-rich surface, usually built with a synthetic surfacing veil, that protects the glass from moisture, chemicals and ultraviolet light and stops fiber blooming. Cutting, drilling, punching or sanding opens that surface. Clean and dry the exposed area, then brush on a catalyzed resin or a polyester, epoxy or polyurethane coating; acrylic lacquer and oil-based paint also seal, but resins give better corrosion resistance. Sanding after sealing reopens the surface.
Sealing matters most outdoors, in water, chemical and electrical service. For parts cut in our factory, ask in the RFQ for the ends and holes to be sealed before packing; the quotation states whether it is included.
Bonding fiberglass: surface preparation and adhesives
A bonded joint is only as good as the surfaces under it. The surface of a pultruded profile carries release agent from the die and a resin-rich veil, and adhesive will not grip either reliably. Use an adhesive whose maker lists it as compatible with fiberglass reinforced polymers: two-part polyurethanes, epoxies and methyl methacrylates are the usual choices. A rigid epoxy suits joints that do not flex; where the joint will bend in service, choose a tougher, more flexible adhesive.
- 01
Clean
Wipe off grease and dirt with a clean cloth dampened with acetone or a similar solvent, then wipe dry. Do not soak or immerse the profile in solvent.
- 02
Sand off the veil
Sand both mating surfaces with 80 grit until the surfacing veil is gone. Power sanding is fine on large areas; keep the pressure light so the resin does not heat.
- 03
Remove the dust
Brush or wipe with a clean dry cloth. Do not wipe with solvent after sanding, and do not handle the prepared surfaces.
- 04
Apply and assemble
Mix only what you can use within the pot life. Spread a thin film on both surfaces, covering any exposed glass. Inside a tube, spread the adhesive with a dowel or rod rolled around the bore, then slide the inner part in.
- 05
Clamp and cure
Hold the joint still and straight with clamps, weights or fasteners. For epoxy adhesives the Strongwell manual gives about 8 hours before careful handling, clamps left on for 20 to 24 hours, and at least 48 hours at 70 °F before the joint carries design load; colder conditions take longer. Wipe squeeze-out into a neat bead before it sets.
Adhesive joints are strongest in compression or tension across the joint, adequate in shear, and weakest in peel. Where a joint will be pried open at one edge, add a mechanical fastener or wrap the joint with fiberglass tape and resin.
Threads in fiberglass
Cutting a thread severs the continuous glass fibers, so the thread is held only by the resin. Threads in fiberglass are acceptable where strength is not important and are improved by bonding the threaded joint with polyester or epoxy adhesive. Cut them with standard taps and dies lubricated with plain water if the joint will be bonded, and leave clearance at the bottom of a blind hole. For a removable connection that must carry load, bond a metal insert into the fiberglass instead.
For non-conductive studs and hangers where the load is modest, see the fiberglass threaded rod sizes
Painting and finishing
Pultruded fiberglass does not need paint for protection, but an outdoor surface fades and can bloom over years of sun. A polyurethane paint improves weathering and appearance; epoxy and urethane paints suit decorative finishes. Clean the surface, lightly sand where the release agent stops paint from wetting, prime if the paint maker asks for it, and keep paint off any surface that sleeves inside another tube: a coat of paint takes up the clearance the fit depends on. For routine cleaning, warm soapy water and a soft brush are enough.
Sleeving and fit guide for our inch sizes
These tables are worked out from the size chart: a part fits inside a tube when its outside size equals the tube's bore or clear opening. Nominal sizes are line-to-line, so a sliding fit needs clearance agreed on the drawing; we set the bore and outside tolerances to it and check the pair on samples. Round parts inside a square tube bear on the flats only. Parts from another maker with the same nominal size may not fit ours.
| Round tube (OD × ID, in) | Fits inside this tube | This tube fits inside |
|---|---|---|
| 1/4 × 9/64 | None listed | 1/2 × 1/4 round tube |
| 3/8 × 3/16 | 3/16 rod | None listed |
| 1/2 × 1/4 | 1/4 × 9/64 round tube; 1/4 rod | 3/4 × 1/2 round tube; 1 × 1/2 round tube |
| 3/4 × 1/2 | 1/2 × 1/4 round tube; 1/2 rod | 1 × 3/4 round tube; 1-1/4 × 3/4 round tube; 1 × 1 × 1/8 square tube |
| 1 × 3/4 | 3/4 × 1/2 round tube; 3/4 rod | 1-1/4 × 1 round tube; 1-1/2 × 1 round tube; 1-1/4 × 1-1/4 × 1/8 square tube |
| 1-1/4 × 1 | 1 × 3/4 round tube; 1 × 1/2 round tube; 1 rod | 1-1/2 × 1-1/4 round tube; 1-3/4 × 1-1/4 round tube; 1-1/2 × 1-1/2 × 1/8 square tube |
| 1-1/2 × 1-1/4 | 1-1/4 × 1 round tube; 1-1/4 × 3/4 round tube; 1-1/4 rod | 1-3/4 × 1-1/2 round tube; 2 × 1-1/2 round tube; 1-3/4 × 1-3/4 × 1/8 square tube; 2 × 2 × 1/4 square tube |
| 1-3/4 × 1-1/2 | 1-1/2 × 1-1/4 round tube; 1-1/2 × 1 round tube; 1-1/2 rod | 2 × 1-3/4 round tube; 2 × 2 × 1/8 square tube |
| 2 × 1-3/4 | 1-3/4 × 1-1/2 round tube; 1-3/4 × 1-1/4 round tube; 1-3/4 rod | 2-1/4 × 2 round tube; 2-1/2 × 2 round tube |
| 2-1/4 × 2 | 2 × 1-3/4 round tube; 2 × 1-1/2 round tube | 2-1/2 × 2-1/4 round tube; 2-1/2 × 2-1/2 × 1/8 square tube |
| 2-1/2 × 2-1/4 | 2-1/4 × 2 round tube | 2-3/4 × 2-1/2 round tube; 3 × 2-1/2 round tube |
| 2-3/4 × 2-1/2 | 2-1/2 × 2-1/4 round tube; 2-1/2 × 2 round tube | 3 × 2-3/4 round tube; 3 × 3 × 1/8 square tube |
| 3 × 2-3/4 | 2-3/4 × 2-1/2 round tube | 3-1/2 × 3 round tube |
| 1 × 1/2 | 1/2 × 1/4 round tube; 1/2 rod | 1-1/4 × 1 round tube; 1-1/2 × 1 round tube; 1-1/4 × 1-1/4 × 1/8 square tube |
| 1-1/4 × 3/4 | 3/4 × 1/2 round tube; 3/4 rod | 1-1/2 × 1-1/4 round tube; 1-3/4 × 1-1/4 round tube; 1-1/2 × 1-1/2 × 1/8 square tube |
| 1-1/2 × 1 | 1 × 3/4 round tube; 1 × 1/2 round tube; 1 rod | 1-3/4 × 1-1/2 round tube; 2 × 1-1/2 round tube; 1-3/4 × 1-3/4 × 1/8 square tube; 2 × 2 × 1/4 square tube |
| 1-3/4 × 1-1/4 | 1-1/4 × 1 round tube; 1-1/4 × 3/4 round tube; 1-1/4 rod | 2 × 1-3/4 round tube; 2 × 2 × 1/8 square tube |
| 2 × 1-1/2 | 1-1/2 × 1-1/4 round tube; 1-1/2 × 1 round tube; 1-1/2 rod | 2-1/4 × 2 round tube; 2-1/2 × 2 round tube |
| 2-1/2 × 2 | 2 × 1-3/4 round tube; 2 × 1-1/2 round tube | 2-3/4 × 2-1/2 round tube; 3 × 2-1/2 round tube |
| 3 × 2-1/2 | 2-1/2 × 2-1/4 round tube; 2-1/2 × 2 round tube | 3-1/2 × 3 round tube |
| 3-1/2 × 3 | 3 × 2-3/4 round tube; 3 × 2-1/2 round tube | 4 × 3-1/2 round tube |
| 4 × 3-1/2 | 3-1/2 × 3 round tube | None listed |
| Square tube (side × side × wall, in) | Fits inside this tube | This tube fits inside |
|---|---|---|
| 1 × 1 × 1/8 | 3/4 square bar; 3/4 × 1/2 round tube; 3/4 rod | 1-1/4 × 1-1/4 × 1/8 square tube |
| 1-1/4 × 1-1/4 × 1/8 | 1 × 1 × 1/8 square tube; 1 square bar; 1 × 3/4 round tube; 1 × 1/2 round tube; 1 rod | 1-1/2 × 1-1/2 × 1/8 square tube |
| 1-1/2 × 1-1/2 × 1/8 | 1-1/4 × 1-1/4 × 1/8 square tube; 1-1/4 square bar; 1-1/4 × 1 round tube; 1-1/4 × 3/4 round tube; 1-1/4 rod | 1-3/4 × 1-3/4 × 1/8 square tube; 2 × 2 × 1/4 square tube |
| 1-3/4 × 1-3/4 × 1/8 | 1-1/2 × 1-1/2 × 1/8 square tube; 1-1/2 × 1-1/2 × 3/16 square tube; 1-1/2 square bar; 1-1/2 × 1-1/4 round tube; 1-1/2 × 1 round tube; 1-1/2 rod | 2 × 2 × 1/8 square tube |
| 2 × 2 × 1/8 | 1-3/4 × 1-3/4 × 1/8 square tube; 1-3/4 × 1-1/2 round tube; 1-3/4 × 1-1/4 round tube; 1-3/4 rod | None listed |
| 2-1/2 × 2-1/2 × 1/8 | 2-1/4 × 2 round tube | None listed |
| 3 × 3 × 1/8 | 2-3/4 × 2-1/2 round tube | None listed |
| 1-1/2 × 1-1/2 × 3/16 | None listed | 1-3/4 × 1-3/4 × 1/8 square tube; 2 × 2 × 1/4 square tube |
| 2 × 2 × 1/4 | 1-1/2 × 1-1/2 × 1/8 square tube; 1-1/2 × 1-1/2 × 3/16 square tube; 1-1/2 square bar; 1-1/2 × 1-1/4 round tube; 1-1/2 × 1 round tube; 1-1/2 rod | None listed |
What our factory can do before shipment
Every order is cut to length at the factory, so parts arrive ready to assemble instead of in mill lengths. Drilling, slotting and other machining to your drawing, sealing of cut ends and holes, and packing nested tubes as matched sets are quoted per drawing as secondary work. Ask for a fit sample of the mating pair before the production run when the joint clearance matters.
- Cut lengths with quantity per length, and the length tolerance you need.
- Hole positions, diameters and slots, dimensioned from a named end and face.
- Which tubes must sleeve together, and whether the fit is sliding, snug or bonded.
- Whether cut ends and holes must be sealed, and the service environment.
- Packing: bundles per length, nested sets, end protection.
Sources and further reading
- Strongwell: Fabrication & Repair Manual for Strongwell FRP (2024)
Source of every tool, grit, tolerance and cure figure on this page: grit-edge and diamond blades, 24 to 32 TPI hacksaw blades, 60 to 80 grit diamond blades for production, no shearing above 3/16 in, drilled holes 0.002 to 0.004 in undersize, No. 30 drill for a 1/8 in rivet, 80 grit removal of the surfacing veil before bonding, epoxy cure times, resin sealing of cut and drilled surfaces, painting.
Questions buyers ask
- Which blade should I use to cut fiberglass tube?
- A carbide or diamond grit-edge blade on a miter, table or band saw. For production cutting the Strongwell manual recommends a 60 to 80 grit diamond blade. Toothed carbide-tipped blades are not recommended because they vibrate and lose teeth.
- Can I cut fiberglass rod with a hacksaw?
- Yes, for a few pieces. Use a blade with 24 to 32 teeth per inch, support the rod on both sides of the cut and wrap the cut line in masking tape to limit splintering.
- What drill bit should I use on fiberglass?
- Carbide-tipped for anything more than a few holes. Drill at about hardwood speed with light pressure and back up the exit side. Holes come out slightly undersize, so drill one size up for a close-fitting pin or rivet.
- How do I join two fiberglass tubes?
- Sleeve the smaller tube into the next size up, then bond it, pin it through both walls, or slot the outer tube and close it with a stainless hose clamp if it must come apart. The fit table on this page lists which of our sizes nest.
- Which glue works on fiberglass?
- A two-part polyurethane, epoxy or methyl methacrylate adhesive that its maker lists as compatible with fiberglass reinforced polymers. Sand off the surfacing veil with 80 grit before bonding; adhesive does not hold reliably on the as-pultruded surface.
- Do I need to seal the cut ends?
- Yes for outdoor, wet, chemical and electrical service. Brush a catalyzed resin or a polyester, epoxy or polyurethane coating onto cut ends and drilled holes to close the exposed glass.
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