How Is a Screw Made? From Wire to Finished Fastener

How a screw is made (clear answer first)

Most modern screws are mass-produced by forming steel wire into a head and shank, then rolling threads into the surface, followed by heat treatment (when required), surface finishing, and inspection. The highest-volume route is: wire → cold heading → thread rolling → heat treat (as needed) → coating/plating → quality control → packaging.

This method is fast, consistent, and waste-efficient because it shapes metal by deformation rather than cutting away material. For specialty screws (exotic alloys, unusual geometries, very small runs), machining may replace some steps, but the core goals stay the same: precise dimensions, strong threads, and controlled surface properties.

Choosing the right raw material

Screw performance starts with material selection. The factory typically receives coiled wire (or rod that will be drawn into wire) matched to the required strength, corrosion resistance, and formability.

Common screw materials and what they’re used for

• Low/medium-carbon steel: economical general-purpose screws; often plated for corrosion resistance.
• Alloy steel: higher strength fasteners; typically requires heat treatment for target hardness.
• Stainless steel (e.g., 18-8 / 304, 316): corrosion resistance; usually not heat treated to very high hardness like alloy steel.
• Brass/aluminum: electrical, cosmetic, or weight-sensitive applications; generally lower strength than steels.

Wire prep that affects consistency

Before forming, wire is often cleaned and lubricated (or coated) so it flows predictably in dies without tearing. Straightness and diameter control matter because small wire variations become bigger variations after forming and threading. In many production environments, wire diameter control on the order of ±0.02 mm to ±0.05 mm (depending on size and standard) is a common target to keep downstream dimensions stable.

Step-by-step: from wire to headed blank

The first major manufacturing stage creates a “blank” (a screw-shaped piece without threads or with partial features) by cold forming. Cold forming strengthens metal through work hardening and enables very high throughput.

Cold heading (forming the head and shank)

In cold heading, a cutoff tool shears a short length of wire, then punches and dies reshape it into the screw head and shank. Multi-station headers can form complex heads (pan, hex, countersunk) and features (flanges, washers, underhead radii) in successive hits. A practical way to visualize scale: high-volume headers commonly operate in the range of 100–400+ parts per minute depending on screw size and complexity.

Driving recess or head features

The driver feature (Phillips, Torx-style, hex socket, square) is typically punched during heading using a shaped punch. This is why recess quality depends heavily on punch wear, lubrication, and alignment. When a recess looks “mushy” or cams out easily, the root cause is often worn tooling or incorrect punch depth.

Thread rolling: how the threads are actually formed

After heading, most screws get their threads by rolling rather than cutting. Thread rolling presses the blank between hardened dies that imprint the helical profile by displacing metal. Rolled threads are typically stronger than cut threads because the grain flow follows the thread shape and the surface is cold-worked instead of being notched by machining.

Two common rolling setups

• Flat-die rolling: two flat dies (one stationary, one reciprocating). Very common for screws and high-speed production.
• Cylindrical-die rolling: round dies that roll the blank through. Often used for larger diameters or specialized thread forms.

What factories control during thread rolling

The key controls are blank diameter (before rolling), die geometry, feed/pressure, and lubrication. If the blank is too large, threads can be overfilled; too small and threads are shallow. In practical QC, factories often track thread pitch accuracy and major/minor diameters using gauges, optical comparators, or automated vision systems—especially for small screws where a tiny pitch error can cause cross-threading.

Heat treatment: turning a formed screw into a strong fastener

Not every screw is heat treated, but many high-strength carbon and alloy steel screws are. Heat treatment typically involves hardening (austenitize and quench) and tempering to reach a target balance of strength and toughness.

Typical targets and why they matter

A practical way to interpret heat treatment is hardness: too soft and threads strip; too hard and the screw may become brittle. Many hardened steel screws land in broad hardness ranges such as HRC 28–45 depending on grade and use-case, while stainless screws often rely more on alloy chemistry and cold work than high hardness.

Common heat-treat pitfalls factories try to prevent

• Distortion: controlled by fixturing, load density, and quench strategy.
• Decarburization: surface carbon loss can weaken thread flanks; atmosphere control reduces risk.
• Hydrogen embrittlement sensitivity: especially relevant when plating hardened steels (managed by process controls and baking when specified).

Finishing and coating: corrosion protection and consistent torque

Finishing is more than aesthetics. Coatings influence corrosion resistance, friction, and how consistent installation torque feels. For many assemblies, controlling friction is what prevents over-torque, snapped heads, or inconsistent clamp load.

Common finishes and what they do

• Zinc plating: general corrosion protection; often paired with passivation/topcoats.
• Phosphate + oil: improves lubricity and reduces galling; common for certain structural or automotive uses.
• Mechanical galvanizing or zinc flake systems: used where thicker protection or specific corrosion specs are required.
• Black oxide: minimal corrosion protection alone; often chosen for appearance and mild lubricity.

Real-world examples of spec-style metrics

Coating requirements are often written in measurable terms. Examples you’ll see in purchase specs include coating thickness targets (commonly in the 5–12 μm range for certain zinc systems, depending on standard) and corrosion test requirements such as salt-spray hours. These numbers vary by standard and application, but the point is consistent: finishing is controlled like any other functional dimension.

Quality control: how manufacturers verify a screw is “right”

Screw QC blends fast go/no-go checks with periodic deeper measurement. High-volume lines often combine inline sensing (vision, force monitoring) with sampling plans for dimensional and mechanical tests.

Dimensional checks you can expect

• Head diameter/height and underhead features: calipers, optical measurement, or gauges.
• Thread fit: GO/NO-GO thread gauges to confirm pitch diameter and functional engagement.
• Length and point geometry: especially important for self-tapping or wood screws.

Mechanical tests commonly used on production lots

1. Hardness testing to confirm heat-treat outcome on hardened grades.
2. Torsional strength (drive-to-failure) to ensure the head/recess won’t fail below expectation.
3. Tensile or wedge tests (when required by standard) to confirm ultimate strength and ductility.
4. Coating adhesion and corrosion tests (when specified), plus thickness measurement.

A practical takeaway: if a supplier can clearly state the gauges and mechanical tests used—and provide lot-level results when requested—that’s a strong signal their process is controlled, not improvised.

How specialty screws are made (machining vs forming)

Not every screw is a good candidate for cold heading and rolling. Very small quantities, highly complex geometries, and certain materials may be produced by CNC machining or by a hybrid approach (machined blank + rolled threads, or machined threads where rolling isn’t feasible).

When machining makes sense

• Prototype and low-volume runs where tooling cost for heading dies isn’t justified.
• Unusual head shapes or integrated features that are difficult to form.
• Alloys that are challenging to cold form or require tight geometric tolerances on multiple features.

Trade-offs to expect

Machining usually increases cost per part and material waste, but it reduces up-front tooling complexity and can hold very specific feature tolerances. Cold forming dominates when the part is standardized and quantities are high, because the per-piece cycle time is extremely low.

Conclusion: the practical way to think about screw manufacturing

If you want a reliable mental model for “how is a screw made,” focus on the functional checkpoints: geometry is formed first, threads are rolled for strength and fit, properties are set by heat treat (if needed), and performance is stabilized by finishing and QC.

When comparing suppliers or processes, ask which route they use (cold headed/rolled vs machined), what tests they run (thread gauges, hardness, torsion), and what finish controls they can document. Those answers usually predict real-world assembly performance better than marketing terms.