Steel Screws Buying Guide: Self-Drilling vs Drywall vs Chipboard — How to Specify Screws by Coating, Point, and Size
Steel screws are bought by the box and specified by three things the box rarely explains well: the point type (which decides whether the screw drills or splits), the coating (which decides whether it survives the weather), and the size (which decides whether it holds). A self-drilling screw fixing roofing to purlins works only if the point and length match the steel thickness behind it. Order drywall screws for roofing and the heads shear off in the first storm.
This guide compares the screw types, coatings, size logic, and a complete RFQ checklist.
Screw Type Comparison
| Type | Point | Best for |
|---|---|---|
| Self-drilling (tek) | Drill point + wings | Steel sheet to steel purlin, roofing and cladding — drills its own hole |
| Drywall screw | Sharp point, bugle head | Gypsum board to steel studs or timber — indoor only |
| Chipboard screw | Sharp point, countersunk | Wood, particle board, furniture |
| Machine screw | Blunt, fine thread | Threaded into nuts or metal inserts |
| Self-tapping | Sharp point, coarse thread | Sheet metal assemblies, ducts, light framing |
Coating Guide
| Coating | Salt-spray life | Use |
|---|---|---|
| Zinc-plated (white/blue) | 24–96 h | Indoor work — drywall, furniture |
| Yellow zinc | 96–200 h | General construction, light outdoor |
| Hot-dip galvanized | 500+ h | Roofing, outdoor steelwork, coastal |
| Ceramic / Ruspert / Dacromet | 500–1500 h | Coastal roofing, long-life specifications |
| Stainless 304 / 316 | Decades | Marine, chemical, coastal façade work |
Size Logic for Self-Drilling Screws
- Rule: drill-point length must exceed total thickness to be drilled, and thread length must engage at least 3 full threads in the base material.
- Steel sheet to purlin (0.5 + 2.0 mm): #12 x 25 mm with #3 point covers most roofing.
- Two sheets to heavy purlin: step up to a #5 point and 38–50 mm length.
- Wings: winged screws clear the sheet before threading — use them on thick steel overlaps.
Head and Drive Types
- Hex washer head: roofing and cladding with an EPDM sealing washer — the standard for exterior steel.
- Bugle head: drywall — sinks flush without tearing the paper face.
- Countersunk / flat: wood and furniture where the head must sit flush.
- Pan head: general metal assemblies, ducts.
- Drive: Phillips, pozi, square, and hex (socket) — confirm the bit so installers are not improvising.
Standards Buyers Quote
- ASTM C1513 / C954: screws for gypsum board and steel studs — the drywall reference.
- DIN 7504 / 7981 / 7982: European self-drilling, self-tapping, and drywall screw dimensions.
- ISO 10666: self-drilling screws — mechanical and performance requirements.
- Ask for coating weight or salt-spray hours on the cert — “galvanized” alone means nothing at the coastal spec level.
Common Applications
- Roofing and wall cladding to steel purlins (self-drilling, HDG or coated).
- Drywall and ceiling systems on light steel framing.
- Furniture, cabinetry, and joinery (chipboard).
- Duct and sheet-metal assemblies (self-tapping).
RFQ Checklist
- Type: self-drilling / drywall / chipboard / self-tapping / machine
- Size: diameter x length (gauge and mm), thread pitch
- Point number (self-drilling #1–#5) and head type
- Coating: zinc / yellow zinc / HDG / ceramic / stainless
- Packing (box, bucket, blister, bulk), quantity, certs, destination / Incoterm
FAQ
What coating for roof screws? Hot-dip galvanized at minimum; use ceramic/Ruspert or stainless within 10 km of the coast.
Why do my screws strip or snap? Point too short for the steel stack-up, or an impact driver overdriving — check length and use a clutch setting.
Are all drywall screws the same? No — phosphate-coated fine-thread for steel studs, coarse-thread for timber, and they are not rated for exterior use.
Why Source Screws from Yihang Metal
Yihang Metal supplies self-drilling, drywall, chipboard, and self-tapping screws in sizes #6–#14 and 3.5–6.3 mm, with zinc, yellow zinc, hot-dip galvanized, ceramic-coated, and stainless finishes, EPDM-washer roofing variants, and packing in boxes, buckets, or bulk cartons for container shipment. Standard orders typically ship in 20–30 days.
Ready to specify your screws? Send us the type, size, point and head, coating, packing, and quantity, and we will confirm availability and lead time with a fixed-price quote. Email [email protected] or use the quote form on this page — our team replies within one business day.