Stainless Steel Anti-Theft Nuts

Function – when to use an anti-theft nut

Use an anti-theft (security) nut when you need to discourage unauthorized removal of parts, especially in:

Public areas – street furniture, lighting poles, sign boards, guard rails, barriers

Outdoor equipment – CCTV poles, solar structures, telecom towers, gates

High-theft risk components – wheels, covers, grating, enclosures, access panels

Security nuts are designed to make removal difficult without special tools or to be one-way (non-removable) after tightening.

Environment & corrosion

Indoors / general outdoor → A2 (304) anti-theft nut

Marine / coastal / chloride / chemical → A4 (316) anti-theft nut

A2 for general structures, poles, fences, indoor & city outdoor use.

A4 for coastal, marine, industrial chemical areas or where long-term corrosion resistance is critical.

As with other stainless fasteners:

If you’re near sea, salt spray, chemical plants, cooling towers → choose A4.

Type of anti-theft nut

Choose the security concept based on how the joint will be used and maintained:

Shear nuts / breakaway nuts

Hex portion used for tightening shears off at a preset torque, leaving a smooth, conical nut underneath.

One-way security: very hard to remove without cutting tools.

Ideal where no future maintenance is expected or access must be strictly controlled.

Special drive / keyed security nuts

Require a matching special key or socket (e.g., pin–torx, multi-lobe, unique key patterns).

Allow removal with the correct tool.

Good where occasional maintenance is required but theft risk must be reduced.

Sleeve / shroud type security nuts

Nut protected by a spinning sleeve or smooth outer shell that prevents standard tools from gripping.

Often used on exposed studs where tools can otherwise easily attack the nut.

Selection thumb rule:

No maintenance, maximum tamper resistance → Shear nut / one-way nut.

Need controlled removal for service → Special-key / sleeve-type security nut.

Strength & matching with bolt/stud

Even though the geometry is different, the basic rules of strength still apply:

Choose an anti-theft nut whose material and property class match the bolt/stud:

With A2-70 bolts/studs → use A2-70 anti-theft nuts.

With A4-70 bolts/studs → use A4-70 anti-theft nuts.

For highly loaded structural joints, confirm that the chosen security nut:

Gives adequate thread engagement, and

Is rated (by supplier/standard) for the required preload/torque.

Often the security shape reduces usable wrenching area, so practical tightening torque may be lower than a conventional hex nut – keep that in mind while designing joints.

Thread form & compatibility

Default is metric coarse thread (e.g., M8×1.25, M10×1.5, M12×1.75).

Use fine threads / UNC / UNF only when matching existing bolts or tapped holes.

Always ensure:

Same diameter, pitch, and thread standard between bolt/stud and anti-theft nut.

For shear nuts, check:

The thread length inside the nut is sufficient for proper engagement with the stud.

Security nuts are usually based on standard stainless steel nut materials (A2 / A4) and property classes (e.g., A2-70, A4-70), but incorporate special shapes or features for tamper resistance.

The locking / security design is in addition to the basic mechanical strength of the nut.

A2-70 Anti-theft nuts

Material: A2 (304) stainless steel

Property class: 70 (compatible with A2-70 bolts/studs)

Typical usage:

City infrastructure, railings, sign boards, street lights, fences, covers

Medium corrosion exposure (urban outdoor, indoor industrial).

A4-70 Anti-theft nuts

Material: A4 (316) stainless steel

Property class: 70 (compatible with A4-70 bolts/studs)

Typical usage:

Marine/coastal installations, ports, piers, seafront railings

Chemical plants, water treatment, poolside environments

Installations where corrosion resistance and tamper-resistance are both critical.

In most designs, anti-theft nuts are treated as structurally equivalent to standard nuts of the same property class, provided thread engagement and tightening practices are correct.

However, due to special shapes (shear head, smooth cone, sleeves), practical torque and tool grip may be different from a normal hex nut – always follow the manufacturer’s tightening recommendations.

Simple selection guide

General outdoor security (sign boards, railings, basic infrastructure) →

→ A2-70 anti-theft nut, shear type where no access is needed, or keyed type for serviceable joints.

Coastal / marine / chemical plants / high corrosion risk →

→ A4-70 anti-theft nut, typically shear or keyed, depending on maintenance requirements.

One-time installation, no removal allowed →

→ Shear / breakaway anti-theft nut matched to bolt material and size.

High theft risk but periodic maintenance required →

→ Keyed or sleeve-type security nut with controlled key/sockets.