Screws for Metal

Self Drilling Screws for Sheet, Section and Plate Metal

Self drilling screws cut their own pilot hole AND tap the thread in a single tool change. The screw point has a drill flute ground into it, the thread starts behind the drill section, and a powered driver sets the whole fastener in one continuous operation. Pre-drilling is eliminated, productivity rises, and the operator never has to swap a drill bit for a fastener driver. Bolt & Nut Australia carries the Cyclone and Series 500 self drilling screw range from Brisbane in 7 head styles across 550+ SKUs covering nearly every sheet-metal and metal-to-metal fastening task in Australian building, fencing, roofing, awning and shed construction.

We've been supplying these online from Brisbane for over 15 years. With 25,000 stock lines and over 200 million pieces in stock, we carry one of the most comprehensive ranges of self drilling screws for metal available in Australia — from hex flange (Cyclone), countersunk, countersunk with wings, wafer, button pan, flat top, bugle plasterboard and Bugle batten decking heads in galvanised and the full COLORBOND painted colour range. Save more as you buy more — we offer up to 13 price breaks plus 3 spend-tier discounts.

MATERIALS AND COATINGS

Galvanised (Class 3, 4, B8 and X9): galvanised finish for exterior structural framing and roof fastening - Class 3 for sheltered exterior, stepping up to Class 4, B8 and X9 for harsher salt or chlorine exposure. The standard exterior finish across the BNA self drilling screw range.

Zinc Yellow (Class 2): zinc plate with a yellow chromate passivation - Class 2 corrosion rating for interior and dry, sheltered fixing. Carries the same 1000+ MPa Class steel core as the galvanised range. For exterior and exposed work, step up to a galvanised Class 3, 4, B8 or X9 finish.

Painted COLORBOND-matched: Wafer-head screws painted to match the full BlueScope COLORBOND colour range (Basalt, Night Sky, Classic Cream, Surfmist, Woodland Grey, Monument and 30+ more). Used for shed and patio cladding, fencing, awnings and any exterior application where the screw head needs to disappear into the cladding colour.

DRILL POINT AND THREAD MATCHING

Self drilling screws are gauged by the substrate steel they can drill through. The drill-point number (Series 500 / Tek 1 through Tek 5) maps to the maximum drill capacity: Tek 1 = up to 1.5mm sheet, Tek 2 = 2.5mm, Tek 3 = 3.5mm, Tek 4 = 5.0mm, Tek 5 = 12.5mm. The thread series (coarse, fine) matches the application - coarse for thin sheet (cladding, shed wall), fine for thicker steel (structural section, purlin).

Gauge (6g, 8g, 10g, 12g, 14g) is the thread diameter - the larger the gauge, the higher the pull-out load. Length covers the cladding thickness plus the host steel - the screw must drill and engage in the host without bottoming out. 6g-20 plasterboard screws are short and fine-threaded for thin sheet; 14g-10 hex flange screws are long and coarse for purlin and structural fastening.

MATCHING POINT TO SUBSTRATE THICKNESS

The most common workshop failure with self drilling screws is point mismatch - the wrong drill point for the gauge of metal being fastened. Too short a point and the thread starts cutting before the drill finishes its hole, stripping the threads in the substrate. Too long a point and the thread can't engage until the drill has cleared the substrate entirely, wasting screw length. Point selection is by total substrate thickness (top sheet plus base steel), not by individual layer.

Point 2 (#2): for total substrate up to 2.0mm. Standard tek for cladding-onto-battens, sheet-on-stud, and light-section connections. Drilling capacity of approximately 1.5mm to 2.0mm steel. The most-stocked point across BNA's range.

Point 3 (#3): for total substrate 2.0 to 3.0mm. Used for cladding onto C-section purlins, sheet onto 2mm to 3mm RHS, and dual-layer steel where the combined thickness is in this range. Drilling capacity approximately 2.5mm to 3.0mm.

Point 4 (#4): for total substrate 3.0 to 4.5mm. Used for cladding onto heavier purlins, 4mm sheet-on-frame, and structural-steel work. Drilling capacity approximately 4.0mm to 4.5mm steel.

Point 5 (#5): for total substrate 4.5 to 6.0mm. Heavy structural connections - fastening cladding or accessories onto 5mm and 6mm steel sections. Drilling capacity approximately 5.0mm to 6.0mm. Use the matched high-torque cordless impact driver - underpowered drivers stall before the drill finishes.

Point 12 (extra-long #5): for fastening 12mm to 20mm of timber spacer onto steel below. The extra-long drill flute clears timber chips while the drill point engages the steel beneath, then the thread bites in the steel. The walling-onto-batten-onto-steel-frame application.

If the total substrate thickness sits right at the boundary between two points (e.g. exactly 2.0mm), step UP to the larger point - the drill capacity is the limiting factor and an undersized drill stalls before clearing the hole. Step down only when you're well below the lower point's minimum and the screw length needs the shorter drill section.

CLADDING AND ROOFING APPLICATIONS

The single largest use of self drilling metal screws is fastening sheet cladding to steel structure - roofing iron onto purlins, walling onto girts, sheet metal onto RHS frames. The screw choice differs by orientation (roof vs wall), exposure (coastal vs inland) and the cladding profile. The rules below cover the standard Australian residential and light-commercial applications.

Roofing iron onto steel purlins: the Hex Flange screw with bonded EPDM sealing washer is the universal choice. 12g x 65mm covers most corrugated and trapezoidal profiles onto 1.5mm to 3mm purlins; 12g x 50mm for shallower profiles. The neoprene-bonded steel washer compresses as the screw drives, sealing the screw entry against water ingress. Fasten through the crown (high rib) of corrugated, through the pan (low rib) of trapezoidal as directed by the cladding spec sheet.

Roofing iron onto timber battens: use the timber roofing screws (Type 17 self drilling tip into timber) with bonded EPDM washer. These are covered in our Screws for Timber category - this self drilling metal screw range targets steel-to-steel connections.

Walling onto girts: the Hex Flange Wall screw (8g x 18mm or 8g x 25mm) is the standard for vertical walling. Smaller head and shorter length than roofing screws - walls don't carry weather load the way roofs do, and the smaller head presents a cleaner wall face. Sealing washers optional on walls; mandatory on roofs.

Stitching screws (sheet-to-sheet): short Hex Flange or Wafer Head screws stitch overlapping cladding sheets along their side-laps. Standard size is 10g or 12g x 16mm to 20mm. The stitch holds the sheet-to-sheet lap closed between the main fastener rows, preventing wind from lifting the lap.

Sealing washer pairing: every roofing screw needs the matched bonded sealing washer. Without the EPDM compression seal, the screw hole becomes a leak path within months. See the Sealing Washers range for bonded EPDM washers in the matched sizes. Most Hex Flange roofing screws ship with the washer pre-fitted; check the product description before purchasing the washer separately.

Cyclonic-zone fastening (Region C / D): Australian cyclonic regions require higher fastener density and the cladding-engineer's specified fastener spec. Don't substitute - the published pull-out load of a 12g roofing screw into 1.5mm purlin is in the engineer's calc. Contact us with the cyclonic specification and we'll match the right product.

COATINGS EXPLAINED — WHAT CLASS 4, B8, DX3, DX4, TYKOTE AND RUSPERT MEAN

Screws come with different coatings to suit different environments. The Australian standard for screws is AS 3566 — the higher the class, the more rust protection. Class 4 is our preferred minimum. We still stock some Class 3 and are slowly moving the range to Class 4. Class 3 is fine for sheds, garages and inland builds. Use Class 4 or higher within 1 km of the coast, or anywhere with salty air, chemicals or industrial pollution.

Class 3 — The long-standing minimum for inland external use. Fine for sheds, garages, rural and suburban inland builds. Still stocked while we transition the range to Class 4.

Class 4 — Heavy-duty zinc with a sealing topcoat. The right choice for coastal builds within 1 km of the surf and most industrial sites. Lasts 15 to 25 years in normal use. Brand variants of Class 4 include Hobson's DX4 (with paint-matched topcoat) and Hobson's X9 (for steel-to-steel and roofing).

Hobson DX3 and DX4 — Hobson's brand names for Class 3 (DX3) and Class 4 (DX4) screws. DX4 comes in paint colours to match Colorbond and standard trade colours. We stock both while we transition the range over to DX4.

Bremick Revolution B8 — Bremick's top coating, twice as protective as Class 4. Built for severe coastal and industrial sites, including beachfront work within 150 metres of breaking surf. Bremick warrants these screws for up to 30 years inland and 10 years on the worst coastal sites. The coating is also 8x harder than Class 4, so it survives the drilling without rubbing off.

Tykote — Hobson's top coating for timber, decking and landscape screws. Built for treated pine, hardwood decking and outdoor timber work in tough coastal or industrial spots. Same protection level as B8 — for timber instead of steel.

Ruspert — A three-layer Japanese coating: zinc + chemical sealer + ceramic top. Comes in three grades — R500, R1000 and R1500. The number is hours of rust testing, so higher means longer life. Handles acid, alkaline chemicals and saltwater better than plain galvanised.

Mechanical Galvanised — Zinc applied cold by tumbling the screws with zinc flakes and glass beads, instead of dipping them in molten zinc. The cold process keeps hardened screws strong (no heat damage). Protection level usually matches Class 4.

What about Class 5? There's no official Class 5 in AS 3566 — the standard stops at Class 4. When you see Class 5 in marketing, it means a coating that goes above Class 4, like B8, Tykote or Ruspert R1000+. We list the actual coating name on each product instead of using a generic Class 5 label.

Which coating for where?

• Inland sheds, garages and rural builds — Class 3 works. Class 4 if you want longer life.
• Suburban or mild industrial areas — Class 4.
• Within 1 km of the surf — Class 4 or higher. Hobson DX4, X9 or Bremick B8 are solid picks.
• Beachfront (within 150 m of breaking surf) or heavy industrial — Bremick B8, Tykote or Ruspert R1000+.
• Not sure? Send us your postcode and we'll match the coating to your site.

View the full coating comparison table ▾

SCREW GAUGE AND TPI

Screws for Metal are sized in Australian / imperial gauge. Each gauge can be stocked with more than one TPI because the same body diameter fastens both thin sheet and thicker steel. The Thread Profile column tags each TPI variant as coarse, fine or in between — coarse threads (lower TPI) are aimed at thinner sheet metal, fine threads (higher TPI) at thicker steel where more thread engagement gives a stronger hold against pull-out. The table below shows the stocked range:

Bolt & Nut Australia stocks 6g, 8g, 10g, 12g and 14g; longer steel sections often pair best with the higher-TPI / fine-profile variants in each gauge row.

OUR RANGE

Hex Flange Metal Screws — Cyclone hex flange self drillers with integrated bonded washer - the workshop standard for roofing, walling and metal-cladding fastening to purlin and structural steel.

Countersunk Metal Screws — flush-seat self drillers for cladding into steel where the screw head needs to sit below the surface for paint, finish or cleaning purposes.

Countersunk with Wings Metal Screws — the same countersunk geometry with under-head wings that ream a clean countersink in timber before the head reaches the steel host. For composite metal-on-timber assemblies.

Button Pan & Wafer Metal Screws — low-profile heads for cladding-to-cladding fastening where a flange head would protrude and snag. Phillips and square drives, Galvanised and Zinc Yellow.

Flat Top Metal Screws — minimum-profile flat-top head for trim and finish work where the screw must lay almost flush with the cladding face.

Painted Metal Screws — COLORBOND-colour-matched wafer head screws for fencing, sheds, patios and exterior cladding where the screw must blend visually with the substrate.

Plasterboard Metal Screws — bugle-head fine-thread self drillers for plasterboard installation onto metal stud framing. Zinc Yellow finish, bugle seats flush in board face.

Screws for Metal Decking — long-shank bugle-batten head self drillers for decking into steel joist - the screw drills the steel batten and seats the batten timber face cleanly in one pass.

Need help choosing the right grade or size? Our Technical PDF's Library has specification guides and technical charts. Prices include GST and free standard delivery anywhere in Australia.

FREQUENTLY ASKED QUESTIONS

How thick a sheet can a self drilling screw cut through?

The drill point number sets the limit. Tek 1 = up to 1.5mm steel, Tek 2 = 2.5mm, Tek 3 = 3.5mm, Tek 4 = 5.0mm, Tek 5 = up to 12.5mm. Cyclone hex flange screws are commonly Tek 4 (BRA / Multiseal designation) - rated for sheet and purlin work up to 5mm. For structural plate above 5mm thickness, the answer is a pre-drilled bolt assembly, not a self driller.

What's the difference between coarse and fine thread on self drilling screws?

Coarse threads have wider spacing (~14 TPI on 10g, ~10 TPI on 14g) - they cut faster and bite better in thin sheet but slip in thicker steel. Fine threads (~24 TPI on 10g) cut slower but hold tighter in heavier steel section. The general rule: coarse for cladding into sheet, fine for fastening into purlin and structural steel section.

Why does my self driller spin without biting?

Three causes - wrong drill point for the host (Tek 1 in 3mm sheet just wears the point), worn drill point from over-use, or too low driver RPM (these need 1500-2500 RPM at the point). Switching to a fresh screw and a higher driver speed fixes 95% of bite failures.

Can I use galvanised self drillers in coastal applications?

For sheltered coastal work yes; for direct sea-spray exposure no. Galvanised Class 3 finish handles inland and sheltered coastal but doesn't survive salt spray. For exposed coastal use, switch to stainless-grade self drillers (limited range) or to Class 4 / Zinc Yellow finish for marginal extension.

Are painted COLORBOND screws full-painted, or only the head?

Only the head is painted - the shank under the cladding is the same galvanised finish as the unpainted range. The visible head is colour-matched to the BlueScope COLORBOND chart so it disappears into the cladding panel when installed. Touch-up paint is available for damaged heads.

What's the difference between a Cyclone screw and a Tek screw?

Cyclone is BNA's brand of self drilling roofing screw, Tek is the original generic patent name (now a generic term in the trade). Cyclone screws use the same Tek-pattern drill point + thread + bonded washer geometry. The Cyclone-branded range carries BRA / Multiseal bonded washer for guaranteed weather seal under the head.

Why does a bonded washer matter on a roofing screw?

The bonded (BRA / Multiseal) washer is a rubber seal vulcanised to a steel washer under the screw head. Driven flat against the cladding it forms a permanent weather seal around the screw shank. Without the bonded washer, every penetration is a leak path. The Cyclone hex flange range has the bonded washer pre-installed.

Can I drive these screws with a standard cordless drill?

Yes, but at the right speed. Self drillers in thin sheet (1-2mm) run at 1500-2500 RPM. In thicker sheet (3-5mm) drop to 800-1500 RPM to keep the drill point cutting rather than just rubbing. An impact driver works for the LENGTH of the screw but may over-torque the bonded washer at the seat - back off the trigger as the head approaches the cladding.

What's the right pilot hole for a self driller in stainless cladding?

Don't pre-drill - the screw is designed to drill its own hole. If you must pre-drill (rare), use a hole 0.5mm smaller than the screw shank to give the thread material to engage. Standard stainless cladding (Colorbond Stainless, 5mm or less) self-drillers cut cleanly without pre-drilling.

Why do my countersunk metal screws crack the timber when I'm fastening through to timber?

Countersunk metal screws are designed for steel-on-steel - they cut a steel countersink with the head. Countersinking INTO timber needs the wings on a countersunk-with-wings variant (the wings ream the timber countersink, then break off when they hit the steel below). Use the right head style for the substrate.

Do COLORBOND-painted screws lose their colour over time?

The screw head paint matches the BlueScope COLORBOND warranty on the cladding sheet - typically 10-15 years colour stability, longer with the premium colours. UV exposure dulls the head paint after 10+ years but the colour shift matches the cladding colour shift, so the visible result stays consistent.

Where can I find the full size, drill capacity and colour chart for the self driller range?

Per-SKU size, drill capacity and finish details are on each sub-cat page. For full product specifications see the Technical PDF's Library library. For the matching paint colours and BlueScope warranty info, BlueScope publishes the COLORBOND chart on the COLORBOND website.

WHY AUSTRALIA TRUSTS BOLT & NUT

With 15+ years selling fasteners online from Brisbane, we hold over 25,000 stock lines and 200 million pieces - 98.75% of online orders placed before 1pm leave same day. Save more as you buy more - we offer up to 13 price breaks plus 3 spend-tier discounts. Read our customer reviews or get in touch if you need help picking the right self drilling metal screw.