Stainless Steel Hex Head Self Drilling Screw

Choosing the Right SS Hex Head Self-Drilling Screw (Guide)
for stainless steel hex head self-drilling screws – roofing / cladding / sheet-to-sheet

1. What is an SS Hex Head Self-Drilling Screw?

An SS hex head self-drilling screw is:

A hexagon head screw (tightened with spanner/socket)

With an integrated self-drilling tip (“drill point”) – no separate drilling/tapping needed for thin sheets

With self-tapping machine-type thread for sheet-to-sheet fixing

Made fully or partially from stainless steel (or with stainless head/washer over carbon steel body in many commercial products)

Used mainly to fasten:

Sheet metal to sheet metal (roofing/cladding)

Sheet metal to purlins / light structural sections

Sandwich panels, roofing sheets, wall cladding, etc.

2. Very Important Reality Check – Stainless vs Drilling

Pure austenitic stainless steel (A2/A4) is not very hard, and self-drilling points need high hardness to drill into metal.
So in practice you usually see:

Carbon steel self-drilling screw with stainless head/washer cap

Drill point & main body: case-hardened carbon steel

Head + washer surface: stainless cap or stainless bonded washer

Good drilling + stainless appearance/top side corrosion resistance

Full stainless screw with special hardened drill point

More expensive

Usually limited in drilling capacity (thin sheets, aluminium, etc.)

Always check with your supplier:

Is it full SS self-drilling or carbon steel self-drilling with SS cap/washer?

Your choice depends on corrosion requirement vs drilling hardness.

3. Application & Joint Type

Use SS hex head self-drilling screws for:

Roofing sheets to purlins (steel/wood)

Wall cladding sheets to purlins

Light steel framing and sheet-metal fabrications

HVAC, ducting supports, cable trays to thin sections (within drilling capacity)

Avoid them when:

You’re fixing into very thick, hard steel beyond rated drilling capacity

Joint is structural / primary load-bearing → then use bolts/anchors as per design codes

You need flush head – then go for CSK/low profile options

4. Environment & “Stainless” Options

You will see three broad types in market:

a) Normal environment (non-coastal, general industrial)

Options:

Carbon steel self-drilling screw with zinc coating + stainless washer

Carbon steel self-drilling with stainless cap head (bi-metal)

A2 (304) self-drilling variants for thin sheet/aluminium

Choose depending on required life and budget.

b) Coastal / marine / chemical / very high corrosion

Prefer:

Bi-metal self-drilling screws:

Stainless body (often A2/A4) + hardened carbon steel drill tip welded on

Or hardened carbon steel core with full stainless encapsulation of head and exposed shank

A4 (316) versions where available for aggressive coastal/chemical atmospheres

Always clarify with supplier:

Corrosion class (C3, C4, C5 etc. if they use ISO 12944-style classification)

Type of washer: stainless with EPDM backing is standard for roofing/cladding.

c) Low-cost, low-demand indoor

Standard carbon steel self-drilling with zinc coating may be enough (not truly “SS”).

If enquiry says “SS Hex Head Self Drilling”, confirm if they accept carbon steel drill body with SS cap, or they demand full SS body.

Mechanical Properties (Guide) – SS Hex Head Self-Drilling Screws

Because there are multiple constructions (carbon steel body + SS cap vs full SS), mechanical properties vary. Think in two blocks:

A. Carbon Steel Self-Drilling Core with SS Cap/Washer (Very Common)

Core material: case-hardened carbon steel

Surface: zinc / alloy coating or encapsulated under stainless cap

Tensile strength: typically in the range of 900–1200 MPa (depends on spec)

Shear capacity: high; suitable for roofing/cladding loadings

Drill point hardness: high, to allow drilling through steel

Corrosion resistance:

On exposed head – good if SS cap is used

On shank in overlap zone – depends on plating; not as corrosion-proof as solid stainless, but acceptable in many roof designs.

B. Full Stainless / Bi-Metal Self-Drilling Screws

Body: A2 (304) or A4 (316) stainless

Drill point: hardened carbon steel tip welded/attached, or specially treated stainless tip

Indicative tensile strength:

A2/A4 bodies similar to A2-70 / A4-70 (~700 MPa tensile)

Corrosion resistance:

For A4: excellent in marine/coastal environments

Notes:

Drilling capacity is often less than carbon steel-only drillers; good for thin sheets, aluminium, light steels.

For very harsh coastal environments, these give best head/surrounding corrosion resistance.

In real use, for roofing/cladding, the limiting factor is often sheet bearing & pull-through and washer sealing, not pure tensile failure of the screw.

Quick Selection Cheat Sheet (For Sales / Site)

Substrate & Thickness

Thin sheet ↔ thin purlin (within drilling capacity) → self-drilling OK

Too thick/hard → pre-drill or use bolts

Environment

Inland, non-aggressive → carbon steel self-drilling with decent coating is usually OK

Coastal / chemical → bi-metal or SS capped head + EPDM washer, ideally A4-grade contact surfaces

Head & Washer

External roofing/cladding → hex head + EPDM bonded washer

Internal/non-sealing → hex head with simple washer may be sufficient

Diameter & Length

Light sheeting → 4.8 mm

Roofing/cladding on purlins → 5.5–6.3 mm

Ensure 3–5 threads beyond purlin after fixing

Assembly

Correct socket, controlled speed

Do not over-tighten / crush washer

Keep screw perpendicular to sheet.