Stainless Steel Hex Coach Screw

Choosing the Right SS Hex Coach Screw (Guide)
for stainless steel hex head coach / lag / wood screws (e.g. DIN 571)

1. Understand What a Hex Coach Screw Is

An SS hex coach screw (also called hex lag screw / hex wood screw) is:

A hexagon head screw

With a tapered, coarse, deep wood-type thread

Designed to be used without a nut, directly into wood, plugs, or plastic.

Use it when you want a strong, heavy-duty connection into wood or wall plugs but still want easy tightening with a spanner or socket.

2. Application & Joint Type
a) Where are SS hex coach screws used?

Choose hex coach screws for:

Timber structures & frames – beams, trusses, supports

Mounting heavy equipment onto wood or plugs in masonry

Fixing base plates / brackets / supports to timber or concrete (with wall plugs or anchors)

Outdoor constructions – pergolas, gates, sign boards, poles, fencing, decking sub-frames

Not ideal for:

Thin sheet metal directly (use self-tapping / machine screws instead)

Precision machine assemblies (use machine screws/bolts + nuts)

3. Environment & Material Grade
a) Choose material by environment

Normal indoor / light outdoor / general industrial
→ A2 (SS 304) hex coach screw
Good balance of corrosion resistance and cost.

Coastal / marine / chemical / high chloride
→ A4 (SS 316) hex coach screw
Superior resistance to pitting, chlorides, and aggressive environments.

Cost-sensitive, non-critical, mild atmosphere
→ SS 202 can be used, but:

Lower corrosion resistance

Avoid near sea, chemicals, or high humidity

b) Matching with other materials

Try to match grade with other stainless items (brackets, plates, nuts, washers).

For galvanized steel structures, stainless is okay but watch for galvanic corrosion in wet, salty environments.

4. Head Style & Drive

Hex head – allows tightening with:

Spanner

Socket

Impact driver with hex socket (careful with torque)

When to choose:

Need high tightening torque → hex head is perfect

Space for spanner/socket is available

You want easier removal & re-use compared to coach bolts with nuts

If space is tight, consider hex socket (Allen) or Torx wood screws instead.

Mechanical Properties (Guide) – SS Hex Coach Screws

Most stainless coach screws are made from austenitic stainless steel in strength classes similar to A2-70 / A4-70. Actual values can vary slightly with size and manufacturer, but typically:

A2-70 (SS 304) Hex Coach Screw

Material: A2 (approx. SS 304)

Strength class: 70

Minimum tensile strength: ≈ 700 MPa

Proof (yield) strength: ≈ 450 MPa

Hardness: around ≤ 210 HB (varies with standard/size)

Temperature range:

Generally safe for ambient to ~300 °C in non-pressure, non-creep applications

Usage:

General outdoor, structural timber connections, brackets, general construction

A4-70 (SS 316) Hex Coach Screw

Material: A4 (approx. SS 316)

Strength class: 70

Minimum tensile strength: ≈ 700 MPa

Proof strength: ≈ 450 MPa

Key advantage:

Much better pitting & crevice corrosion resistance in chloride-rich environments

Usage:

Coastal / marine, chemical plants, food & pharma installations, wash-down areas

Higher Strength (A4-80 etc.)

Less common for coach screws, but where available:

Tensile strength: ≈ 800 MPa

Proof strength: ≈ 600 MPa

Note: The timber or plug often becomes the weak point before the fastener itself.

Quick Selection Shortcut (Field Use)

Environment

Normal → A2-70 (SS 304)

Marine/chemical/coastal → A4-70 (SS 316)

Diameter

Light brackets → M6–M8

Heavy supports / equipment → M10–M12

Length

Aim for 6–8 × d embedment into timber / plug.

Substrate

Direct into wood → pilot hole (0.6–0.8 × d)

Into concrete → use proper plug or chemical anchor.

Accessories

Always use flat or square plate washer under the hex head for heavy-duty joints.