Sandwich Panel Self-Drilling Screws with EPDM Washer
Product Introduction
We've been making fasteners for export since the early 2000s, and panel screws are one of those products we know inside out. The problem this screw solves is simple: sandwich panels are great at insulation but terrible at holding fasteners. Soft facing, fragile foam core, and a steel purlin hiding underneath. Ordinary screws either rip through the skin or strip out of the thin steel.
So we make the screw differently. The upper thread is coarse — it bites the panel facing without tearing it. The lower thread is fine and sharp, so it gets real purchase in a 1.5 mm purlin and stays put when the wind starts working the roof. And the drill point? That's a #5, about 14 mm of hardened flute. It cuts its own hole through steel up to 12 mm thick. No pilot drilling, no swarf to clean, no second tool on the ladder.
Every screw gets an EPDM washer bonded to a galvanised steel disc, assembled at the factory, not on site. That's the part that stops a roof leaking three years down the line, when the panel skin has expanded and contracted a hundred times. EPDM takes that movement and keeps sealing from −40 °C to +120 °C.
Everything here is made to ISO 15480:2019, grade A, and hardened to ISO 10666:1999 — surface 530 HV minimum, core 320–400 HV. That hardness combination is what lets the point drill and the thread form without the screw snapping. We test it, we batch-check it, and if you want the test reports, you get them. This is a screw for people who have been burned by cheap imports before. We'd rather you order once and not have to think about it again.
Full Specification
Thread data — ST series (ISO 1478)
| Thread size | Pitch P (mm) | Core Ø min (mm) | Core Ø max (mm) | Outside Ø min (mm) | Outside Ø max (mm) |
|---|---|---|---|---|---|
| ST 2.9 | 1.1 | 2.08 | 2.18 | 2.76 | 2.90 |
| ST 3.5 | 1.3 | 2.51 | 2.64 | 3.35 | 3.53 |
| ST 4.2 | 1.4 | 2.95 | 3.10 | 4.04 | 4.22 |
| ST 4.8 | 1.6 | 3.43 | 3.58 | 4.62 | 4.80 |
| ST 5.5 | 1.8 | 3.99 | 4.17 | 5.28 | 5.46 |
| ST 6.3 | 1.8 | 4.70 | 4.88 | 6.03 | 6.25 |
Most sandwich panel screws ship in the ST 5.5 / ST 6.3 range. Nominal size follows the upper (panel) thread — e.g. 6.3 × 130 mm.
Hardness & case depth (ISO 10666:1999)
| Property | Requirement |
|---|---|
| Surface hardness | ≥ 530 HV 0.3 (minimum, after heat treatment) |
| Core hardness, threads ≤ ST 4.2 | 320–400 HV 5 |
| Core hardness, threads > ST 4.2 | 320–400 HV 10 |
| Thread size | Case depth min (mm) | Case depth max (mm) |
|---|---|---|
| ST 2.9 – ST 3.5 | 0.05 | 0.18 |
| ST 4.2 – ST 5.5 | 0.10 | 0.23 |
| ST 6.3 | 0.15 | 0.28 |
EPDM sealing washer
| Parameter | Specification |
|---|---|
| Construction | Steel disc with vulcanised EPDM sealing layer, factory pre-assembled |
| Washer Ø | ≈ 14–19 mm (16 mm standard; 19 mm stainless / marine) |
| Function | Weather seal at the fixing point · compensates thermal movement of the panel skin · resists ageing, ozone and UV |
| Service temperature | −40 °C to +120 °C (continuous) |
| Colour | Black (standard), grey, white, RAL-matched on request |
Surface finishes & corrosion protection
| Finish | Typical use | Notes |
|---|---|---|
| Electroplated zinc (clear/yellow) | Dry interior applications | Standard economical finish |
| Hot-dip galvanised (HDG) | Outdoor, humid atmospheres | Coating thickness per application standard |
| Zinc flake Zn/Al (Dacromet / Ruspert-type) | Coastal, high-corrosion, bolted-clamp conditions | No hydrogen embrittlement risk; superior salt-spray performance |
| Stainless A2 (304) / A4 (316) | Marine and chemically aggressive environments | A4 recommended where chlorides are present |
Size Chart & Length Selection
Standard range — 6.3 mm diameter (12 mm drill)
| Diameter × Length (mm) | Drilling capacity | Packaging (typical) |
|---|---|---|
| 6.3 × 70 | 12 mm (steel base) | 100 pcs / box |
| 6.3 × 90 | ||
| 6.3 × 110 | ||
| 6.3 × 130 | ||
| 6.3 × 150 | ||
| 6.3 × 175 | ||
| 6.3 × 185 | ||
| 6.3 × 210 | ||
| 6.3 × 235 | ||
| 6.3 × 255 |
Shorter series (4.8 / 5.5 mm diameter, lengths from 60 mm, 6 mm drilling capacity) cover thin-gauge substructures and lighter panels.
Panel thickness vs. screw length
| Screw, 6 mm drill (mm) | Panel thickness (mm) | Screw, 12 mm drill (mm) | Panel thickness (mm) |
|---|---|---|---|
| 60 | 13–35 | 70 | 15–35 |
| 80 | 25–55 | 90 | 25–55 |
| 100 | 45–75 | 110 | 45–75 |
| 120 | 45–95 | 130 | 45–95 |
| 140 | 65–115 | 150 | 65–115 |
| 165 | 90–140 | 175 | 90–140 |
| 175 | 100–150 | 185 | 100–150 |
| 200 | 125–175 | 210 | 125–175 |
Three checks when picking length: (1) full thread engagement in the steel base — at least one pitch beyond the section; (2) enough thread bearing in the panel facing; (3) clearance in the foam core so the point doesn't bottom out against the far skin.
Pain Points & Solutions
|
Pain Point |
How Fasto Solves It |
|
Screw heads strip out before full engagement in cold-rolled steel |
We heat-treat 410SS to HRC 38-45. That's hard enough to drive the thread into CRS without the Phillips recess camming out. Our #2 recess geometry is ISO 7049 compliant — not some worn-out tooling. |
|
Truss head pulls through thin sheet metal under vibration |
Our head diameter is 0.350-0.362". That's a 40% larger bearing area than a standard pan head. For really thin material (24-26 ga), we recommend adding a backing washer — but honestly, most installs don't need it. |
|
Rust spotting after 6 months in semi-outdoor conditions |
410SS will tea-stain in wet environments. That's the tradeoff for hardness. But our passivation process (ASTM A967 nitric acid) maximizes the chromium oxide layer. For fully outdoor exposure, we'll tell you straight — use 304 or 316. For sheltered outdoor or indoor, this grade does the job. |
|
Inconsistent thread formation causes cross-threading in production |
We roll threads, don't cut them. Rolled threads are stronger by 20-30% and the surface finish is smoother. Our thread rolling dies get replaced on a fixed-cycle schedule, not when they fail. You get consistent thread geometry batch after batch. |
|
Screws won't start in harder sheet metal without walking or skating |
Type A sharp point with a 40-45° included angle. It bites and stays put. For material over 1.5mm thickness, drill a 3.3-3.5mm pilot hole. It's physics, not magic. |
|
Galvanic corrosion when used with aluminum panels |
Roof and panel contractors don't have one problem with these screws — they have five or six, and they all cost money on site. Here's what we hear, and what the screw does about it. Pre-drilling eats the labour budget
Drilling, then tapping, then fastening means three steps per fixing and a second man on the ladder. Fix: the #5 point drills, taps and seats in one operation. Up to 12 mm of steel, no pilot hole.
Water finds every fixing point
A roof only leaks where it's fastened. Fix: vulcanised EPDM bonded to a galvanised steel disc, pre-assembled at the factory, compresses evenly around the hole and stays elastic from −40 °C to +120 °C.
Screws back out under wind vibration
A single coarse thread loses grip in thin steel and walks loose over time. Fix: the fine-pitch lower thread (d2 5.5 mm) engages the purlin hard and resists self-loosening — the reason double-thread panel screws exist.
Soft panel skin tears and pulls through
A small head punches straight through the facing. Fix: hexagon washer head with an integral flange spreads the clamping force over a wide bearing area and stops pull-through.
Rust at the coast — fast
Salt air finds electroplated zinc in a season. Fix: zinc flake Zn/Al (no hydrogen embrittlement risk) or A4 stainless where chlorides are present. We'll match the finish to your exposure class.
Drill points snap on thick steel
Push a point past its rating and it shears. Fix: the 6.3 mm point is rated to 12 mm structural steel; beyond 12.5 mm we supply special heavy-duty points. Match the point to the section and it won't break.
Wrong length = rework on the roof
Too short means no bite in the steel; too long means a visible point. Fix: our length selection table matches panel thickness to screw length — 50 mm panel, 90 mm screw, done.
Mineral wool cores get chewed up
Standard threads tear fibrous cores during driving. Fix: reduced-thread washer and point designs for mineral wool panels. Tell us the core material and we'll configure it.
Stainless vs. galvanised — galvanic trouble
Bare austenitic stainless against zinc or aluminium can corrode fast in humid air. Fix: bimetal construction (hardened point + corrosion-resistant shank) or coated designs for mixed-material contact.
|
Applications
- Cold-storage & freezer buildings — EPDM holds its seal at −40 °C, which is what freezer service demands
- Clean rooms & hygienic production areas
- Industrial halls & warehouses
- Roof and facade cladding on cold-formed steel purlins and structural sections
- Modular prefabricated buildings
Where we see them go in Latin America
- Cold chain logistics hubs — Brazil and Chile are building freezer warehouses hard, and panel-to-steel fixing is the critical joint in those buildings
- Meat, dairy and seafood processing plants — clean-room grade paneling, where a leaking fixing point means a failed hygiene audit
- Industrial parks — Mexico's manufacturing corridors run on metal-clad halls, and contractors there buy in truckloads
- Roof retrofits — replacing corroded fasteners on existing sandwich roofs without stripping the panel
Why Work With Us?
20+ years in fasteners
We've exported screws, bolts, nuts, nails and rivets for over two decades. Panel screws aren't a side line for us — they're a core product with a dedicated production line.
Our own factory
No trading house in the middle. Heat treatment, threading and washer assembly happen under one roof, so batches stay consistent and lead times stay short.
Certified process
ISO 9001 and IATF 16949 quality systems. Product certificates cover CE, SGS and RoHS. Test reports, mill certs and batch records go out with your shipment if you want them.
Standards-first engineering
We spec to current ISO / EN / ASTM only. DIN 7504 is withdrawn and we won't print it on a drawing. If your project needs an ETA or DoP, ask us — we'll work through it with you.
These aren't hypothetical. Every one of these came from a customer who was losing money before they called us.
FAQ:
Q1: Do sandwich panel screws need a pre-drilled hole?
No. Within the rated capacity of the point — up to 12 mm of steel for the 6.3 mm version — the screw drills, taps and fastens in one pass. That's the whole point of a self-drilling screw.
Q2: How much steel can the 6.3 mm screw drill through?
The standard point drills structural steel up to 12 mm (working range roughly 4–12 mm). Thinner-base versions cover 4–6 mm. Above 12.5 mm you need a special heavy-duty point — we'll flag it on the quote rather than let you find out on site.
Q3: What length screw for a 50 mm sandwich panel?
With the 12 mm drill series, use the 90 mm screw — it covers panels from 25 to 55 mm. The rule: full thread engagement in the steel base, enough thread bearing in the facing, and clearance in the core.
Q4: Why do panel screws come with an EPDM washer?
The vulcanised EPDM layer seals the fixing point against rain, absorbs the thermal movement of the panel skin, and shrugs off ozone and UV. It's the difference between a roof that leaks and one that doesn't. Skip it and you'll find out which one you've built.
Q5: Panel screw vs. normal self-drilling screw — what's the difference?
A panel screw carries a double thread: a coarse upper thread that grips the soft facing without tearing it, and a fine-pitch lower thread that gets real purchase in thin steel and resists vibration loosening. Add the larger flange head and the sealing washer, and you have a fastener built for insulated panels specifically.
Q6: Which finish for coastal or humid climates?
Coastal exposure calls for zinc flake Zn/Al — no hydrogen embrittlement risk and strong salt-spray performance — or A4 stainless where chlorides are present. We'll also flag the galvanic couple: stainless against galvanised steel or aluminium needs a bimetal or coated design in humid air.
Q7:Can these screws handle mineral wool panels?
Yes, with the right configuration. Mineral wool cores need a reduced thread section on the washer and point so the driving action doesn't tear the fibre. Name the core material in your enquiry and we'll spec it correctly the first time.
Q8: Do you supply for cold-storage and freezer buildings?
That's one of our main applications. EPDM stays flexible from −40 °C to +120 °C, which covers freezer service without cracking. Cold chain projects in Brazil, Chile and Mexico are routine for us — send the panel spec and we'll confirm lengths and quantities.