304 SS Hex Flange Self-Drilling Screw with EPDM Washer for Metal Roofing

Product Introduction

You've watched crews slow down on a roof job to pre-drill every hole, swap bits, then come back with a driver. This screw kills those three steps down to one. The drill point bites through sheet steel, the threads cut their own path, and the hex flange head seats the washer the moment torque comes up. Under that flange sits an EPDM washer, bonded on in our factory — not tossed loose in the box, not something your guy has to fish out of his pocket halfway up a ladder.

Why 304? Because a coating eventually stops being a coating. Zinc-plated screws look fine on day one, then start bleeding rust streaks down your cladding within a couple of seasons in humid weather. 304 carries its own chromium oxide film, and we passivate every batch per ASTM A967 to keep that film even and free of iron contamination from forming and handling. One honest limit: if the project sits within a few kilometers of the ocean or sees constant salt spray, step up to A4 (316). We'd rather tell you that before you order than have you find out on a roof.

Buyers ask about the magnet thing, so let's get it out of the way. Yes, the drill point and threads are slightly magnetic. 304 is austenitic and normally non-magnetic — cold forming work-hardens the tip, which is exactly what gives it the hardness to cut steel in the first place. That local magnetism is a sign the tip was formed properly, not a sign of bad material. Corrosion performance doesn't change.

Roofing crews in Brazil and Chile use these on trapezoidal sheets, on purlins, on ag buildings and warehouse shells. Same screw drills, taps, and seals, which matters when you're paying by the hour. Sizes run from ST4.2 for light sheet work up to ST6.3 for roof and purlin builds, with drill ranges checked against the actual stack-up thickness before we quote.

Full Specification

1 Mechanical Properties(A2-70, ISO 3506-1)

2 Chemical Composition-304 (ASTM A240, mass %)

3 Standards System

4 EPDM Sealing Washer — Typical Performance

Actual values per supplier test report. The washer also isolates the screw head from the base metal — a useful galvanic corrosion barrier.

5 Drill Range (Total Sheet Thickness, Low-Carbon Steel)

Example stack: 0.5 mm steel sheet + 2.0 mm purlin = 2.5 mm total — ST5.5 (1.75–5.25 mm) or ST6.3 both work. Range refers to low-carbon steel (e.g. Q235). High-strength steel, stainless base, or over-range thickness: pre-drill, or the point burns or snaps.

Size Chart

Applications

Where These Screws Are Used

• Metal roofing and wall systems — trapezoidal sheets, corrugated panels, standing-seam covers (drive into the wave crest)
• Light steel building envelopes — steel-frame workshops, warehouses, farm buildings, prefab site cabins
• Ventilation ducting, dust extraction systems, equipment enclosure sheet metal
• Solar mounting frames (inland sites) and sign / billboard frames
• Containers, truck bodies, fencing, and outdoor garden structures

Selection Notes for South American Projects

• Roof fixing: ST5.5 or ST6.3 — stiffness and sealing in one screw.
• Thin sheet / cladding work: ST4.2 keeps the bite light.
• Coastal Chile, coastal Peru, and beach-adjacent Brazilian sites: step the whole spec up to A4 (316). Ask for the 316 quotation — it's a standard line for us, not a special.
• High-seismic zones (Chile, Peru, Andean Colombia): hex flange spreads the load and resists vibration loosening better than a plain hex head.

Why Fasto

Twenty-plus Years of Fastener Exports, One Factory

Fasto has been making and exporting screws, bolts, nuts, nails, and rivets for more than two decades. We own the factory — no trading middleman, no batch bought from whoever quoted lowest this month. When you order from us, the cold header, the thread roller, and the inspection bench are all under one roof, and the guy signing the certificate knows which machine ran your lot.

Certification You Can Put in the File

What QC Actually Happens on Your Batch

• Raw material: heat number traceability, spectral chemical spot checks, mechanical property verification (MTC + incoming inspection).
• Cold heading / thread rolling: dimensional tolerances, thread accuracy, drill point form integrity per ISO 15480 / ISO 1478.
• Drilling function: ISO 10666 drilling tests and failure torque tests — the point has to drill or it doesn't ship.
• Surface: passivation film quality (blue spot test), appearance, no free iron per ASTM A967.
• Washer assembly: EPDM pre-fit security, no ring-off, no damage.
• Corrosion: neutral salt spray testing per ISO 9227 when the order calls for it (e.g. 48–72 h).
• Final: full dimensional sampling, thread go/no-go gauges, hardness per ISO 3269.

We don't promise salt spray hours we haven't measured. If a customer needs a number, we run the test and send the report with the batch.

Straight Answers, Even When It Costs Us

We've turned away 304 orders for coastal projects and pushed the 316 upgrade instead. We tell buyers when a screw is over-spec for their job. That sounds like bad salesmanship; it's how you keep a roof standing for fifteen years and keep the customer for the next fifteen.

Pain Points & Solutions

1. Roof leaks around screw holes  —  infiltração / filtración

Driving into the sheet valley, overtightening until the washer squirts out sideways, or using a plain self-tapping screw with no seal — all three end in a wet warehouse floor. Our fix: bonded EPDM washer, drive into the wave crest, and stop when the washer edge just squeezes out evenly. Drill phase 1800–2500 rpm, then drop to 600–1200 rpm for seating.

2. Rust streaks on the cladding  —  parafuso enferruja / tornillo se oxida

Cheap galvanized screws bleed brown lines down the sheet inside two or three wet seasons. That's a coating failing, not a fastener doing its job. Our 304 body carries its own passive film and gets passivated per ASTM A967 before packing. Also watch out: a lot of "inox" roofing screws on the local market are 410 martensitic — hard, cheap, and far less corrosion resistant. Ours is 304, full stop.

3. Drill point snapping or burning  —  ponta broca quebra / punta se quema

Usually three causes: total stack thickness beyond the drill range, spindle speed too high, or the driver tilted off vertical. The point overheats, softens, and snaps. We publish the drill ranges (ST6.3: 2.0–6.0 mm) and the speed discipline in the datasheet, and we'll size the screw for your stack before you order.

4. The pre-drilling hassle  —  precisa furar antes? / ¿necesito pre-perforar?

Standard self-tapping screws need a pilot hole — an extra drill, an extra bit, extra minutes on every fixing. Our self-drilling point does hole, thread, and seat in one pass, verified by ISO 10666 function tests. Pre-drill only when the stack exceeds the range or the base material is stainless / high-strength steel.

5. Washer cracking under the sun  —  borracha resseca / arandela se reseca

NBR and SBR washers go hard and crack after a few years of UV. EPDM is one of the best weather-resistant rubbers there is — UV, ozone, humidity — with a 15–25 year roof service life depending on formulation and environment. Keep it away from mineral oil and gasoline, and control the torque; overtightening is what kills washers, not sunshine.

6. Galvanic corrosion with zinc or aluminum  —  corrosão galvânica / corrosión galvánica

Stainless against galvanized or aluminum, with rain or condensation in the joint, makes a battery — stainless is the cathode and the zinc or aluminum pays for it. The EPDM washer insulates the head contact, which helps. For the threaded joint, keep the assembly dry where you can, or move to a same-family material spec for permanently wet connections.

7. Labor cost eating the job  —  mão de obra / mano de obra

On a big roof, ten extra seconds per screw is a full day of wages. One-pass drilling, an 8/10 mm socket or hex bit drive, no cross-slot cam-out — crews notice the difference by lunchtime. The hex flange also spreads load, so thin sheets don't crush or dimple.

8. "Why is my 304 screw magnetic?"  —  magnetismo / ¿por qué es magnético?

Cold forming work-hardens the drill point and threads (strain-induced martensite). That's the source of the hardness that lets the tip cut steel — and yes, it's slightly magnetic. Normal, expected, and it doesn't change corrosion performance. If a customer rejects a batch over this, send them our datasheet note; it happens a few times a year.

9. Size confusion on site  —  qual tamanho? / ¿qué medida?

Too short and the threads barely engage; too long and the point punches through the purlin. Rule: total stack (sheet + purlin + spacer) inside the drill range, plus 2–3 threads of extension. We supply a sizing table and will confirm your sizes from the drawing — no guesswork.

10. Coastal salt — the honest boundary  —  região de praia / zona costera

304 handles humid inland air, rain, and normal industrial atmospheres well. Within about 5 km of the sea, or under constant salt spray, 304 pits. That's physics, not a defect. For coastal projects we quote A4 (316) — about 30–50% more, and worth every centavo when the alternative is replacing roof fixings on a beach house.