FASTENER TECHNICAL SERIES

2026-10-22

Executive Summary

The Ruspert composite washer drilling screw is a premium self-drilling screw engineered for metal-to-metal and metal-to-timber fastening in aggressive outdoor environments. By combining a case-hardened steel screw body, a drill point that performs one-step drilling and tapping, and a bonded EPDM composite sealing washer, this screw family is built for long-life anti-rust performance.

Protected by the Ruspert ceramic-organic anti-rust coating, the screws deliver up to 1,000+ hours of salt spray resistance without red rust — far exceeding conventional electro-plated screws. This article explains the screw structure, the corrosion protection technology behind the coating, verified anti-rust test data, and practical selection and installation guidance for roofing, cladding, and solar mounting projects.

1. What Is a Composite Washer Drilling Screw?

A composite washer drilling screw (also called a self-drilling screw with bonded sealing washer) is a threaded fastener that performs three operations in a single driving action: drilling, thread-forming, and sealing. Unlike ordinary self-tapping screws, the integrated drill point removes the need for pre-drilling.

The vulcanized EPDM rubber washer — bonded to a galvanized steel backing cap — compresses against the panel surface to form a weather-tight, leak-proof seal.

In plain terms: one screw replaces a drill bit, a tapping screw, and a separate rubber washer — and it keeps rust and rainwater out for years.

The product family typically covers:

Hex washer head (HWH) drilling screws— the roofing industry standard
Countersunk (flat head) drilling screws— for flush-finish applications
Pan / button head drilling screws— for sheet metal and ductwork

2.Anatomy of the Screw

Component	Material & Design	Function
Head	Hex washer head with serrated flange (or countersunk)	High torque transmission; flange distributes the clamping load
Composite washer	EPDM rubber vulcanized to a zinc-plated / 304 stainless steel cap	Weather-tight seal; absorbs vibration; UV and ozone resistant, −40 °C to +120 °C service
Shank & thread	Case-hardened carbon steel (C1022A), rolled thread	High thread-forming strength; rolled threads increase fatigue resistance
Drill point	Hardened drill tip, HRC 55–60	Drills through steel up to 6.0 mm thick in one operation
Coating	Ruspert ceramic-organic composite coating	Long-life anti-rust and anti-corrosion barrier

Product standards: GB/T 15856.4 / DIN 7504K (hex flange head self-drilling screws); thread per GB/T 5280 / ISO 1478.

3.Ruspert Coating: Ceramic-Organic Anti-Corrosion Technology

Barrier protection— the plate-like metal flakes create a tortuous path that blocks water, oxygen, and chloride ions from reaching the steel substrate.
Sacrificial protection— the zinc component corrodes preferentially, providing galvanic (cathodic) protection even if the coating is scratched at the drill point or thread crests.
No hydrogen embrittlement risk— unlike electro-plating, Ruspert is a non-electrolytic dip-spin process, so there is no hydrogen charging of the hardened screw body.
Dimensional stability— the coating builds only 6–12 µm of thickness, so threads keep their gauge and assemble smoothly without re-tapping.

Compared with common screw finishes, Ruspert sits at the top tier of cost-effective corrosion protection:

Finish	Typical Salt Spray to Red Rust (ISO 9227 / ASTM B117)	Relative Cost	Notes
White / blue zinc plating	24–72 h	Low	Indoor or dry interior use only
Yellow zinc plating	72–120 h	Low–Medium	Light outdoor exposure
Mechanical galvanizing	240–400 h	Medium	Good for coastal fasteners
Dacromet / zinc flake (basic)	480–720 h	Medium–High	Chrome-free options available
Ruspert 500	500 h, no red rust	Medium–High	Standard outdoor roofing grade

4. Conclusion

For outdoor screw fastening where rust is the enemy, the Ruspert composite washer drilling screw offers a rare combination: drill-point convenience, EPDM sealing, and ceramic-organic anti-corrosion technology rated to 1,000+ hours of salt spray endurance. It extends the service life of the fastened joint to match — and often outlast — the roofing or cladding system itself, cutting maintenance cycles and total cost of ownership.

For technical datasheets, salt spray test reports, and custom screw specifications, contact our export team.

Prev. Next.

Dacromet-Coated Hex Bolts