Cold Heading Wire for Self-Tapping and Self-Drilling Screws

Self-tapping and self-drilling screws have a specific material challenge: the finished screw needs a hard, sharp thread-forming tip that can cut into metal, plus a tough core that won’t snap under installation torque. That combination — hard surface, tough core — is achieved through case-hardening after the screw is cold-headed and thread-rolled.

The wire grade selection has to support both ends of that requirement: cold heading without cracking, and case-hardening without through-hardening to brittleness.

What case-hardening means for grade selection

Case-hardening (carburization) diffuses carbon into the surface of a steel part, then heat-treats it to produce a hard surface layer over a softer core. For this to work, the base steel needs to be:

• Low enough in carbon to take up additional carbon in the carburizing atmosphere
• High enough in manganese to give the case adequate hardenability
• Clean enough in chemistry to produce predictable case depth and consistent surface hardness

The standard CHQ grades for self-tapping and self-drilling screw production:

C1018 — most common

Excellent carburization response. Cold-heads easily for most screw geometries. The default choice for the majority of self-tapping screws.

C1022 — when more core strength is needed

Higher carbon and manganese than C1018. Produces greater core hardness after case-hardening, useful for larger or higher-load self-tapping screws. Slightly less formable than C1018 — verify your part geometry supports it.

10B21 — for through-hardened applications

If the screw needs to be through-hardened (not just case-hardened), 10B21’s boron-enhanced hardenability is the right choice. Common for heavier self-drilling screws used in steel decking and structural applications.

Cold heading considerations for thread-forming screws

The head geometry of self-tapping screws is often more aggressive than standard fasteners — pan heads, truss heads, hex washer heads, button heads all involve significant material flow during heading. Two practical implications:

Consider material condition carefully. Most self-tapping screw production runs on SAIP material — the tighter dimensional tolerances suit high-speed automated headers, and the moderate part geometries don’t require SAFS’s maximum formability. For unusually aggressive head geometries (deep socket drives, complex flanges), SAFS may be the better choice. The $2/cwt difference is small compared to the cost of die failures from under-formability.

Confirm wire size early. Self-tapping screws often use slightly larger wire diameters than nominal thread size suggests, to give enough material for both the head and the thread-forming tip geometry. Mistakes here are expensive — order a sample lot before committing to a full mill run.

Quality requirements for self-drilling tips

Self-drilling screws have an additional requirement: the drilling tip must maintain a sharp cutting edge through hundreds of installations. This demands:

• Tight inclusion control — non-metallic inclusions create weak points that cause tip failure
• Consistent case depth — variable case depth produces variable cutting performance
• Mill-cert traceability — failures need to be diagnosable, which requires knowing which heat made which screw

Nevers maintains chemistry records on every coil and provides mill certs with every shipment as a standard practice. For high-volume self-drilling production, ask about heat-by-heat segregation — we can stage material from a single heat for production runs requiring consistent properties.

Why buyers source self-tapping wire from Nevers

• Most-stocked grades for the application. C1018, C1022, and 10B21 are core inventory in the diameters self-tapping screw manufacturers use
• SAFS and SAIP both stocked across all three grades
• USA-melt material with full traceability for OEM and defense supply chain
• CHQ specialization since 1977 — we understand the material requirements of self-tapping screw production specifically

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Frequently Asked Questions

What’s the best wire grade for self-tapping screws? C1018 is the most common choice for general-purpose self-tapping screws. For higher-load applications or when more core hardness is needed after case-hardening, C1022 is the next step up. Both are case-hardened after forming to produce a hard thread-forming surface with a tough core.

Do self-drilling screws require a different grade than self-tapping? Often yes. Self-drilling screws — particularly those used in heavier materials or structural applications — frequently use 10B21 for its better hardenability. Lighter-duty self-drilling screws can use C1018 or C1022 with appropriate heat treatment.

Why is case-hardening preferred over through-hardening for self-tapping screws? Self-tapping screws need a sharp, hard thread-forming tip but also need a tough core that won’t snap under installation torque. Through-hardening makes the whole screw hard but brittle. Case-hardening produces the hard surface where it’s needed (thread-forming) while keeping the core ductile.

What’s the typical case depth for self-tapping screws? Effective case depth (to 50 HRC) is typically 0.003” to 0.008” for self-tapping screws, depending on screw size and application. Self-drilling screws often have deeper case depths (0.005” to 0.012”) to support the drilling tip life. Specific case depth requirements are typically set by the screw manufacturer’s quality program.

Does Nevers stock C1018 and C1022 in both SAFS and SAIP conditions? C1022 is stocked in both SAFS (default) and SAIP (+$2/cwt) conditions. C1018 is available on special order — not stocked at our Rockford warehouse. For C1018 requirements, contact us with your size and quantity and we’ll quote sourcing and lead time.

Can you provide single-heat material for self-drilling screw production runs? Yes, when stocked quantities permit. Ask about heat-by-heat segregation when requesting a quote. We maintain heat-level traceability and can stage material for production runs requiring consistent properties.