Metric Flat Head Socket Pipe Plugs (DIN 908) — Marine Stainless Steel A4 (SUS316)

FULLERKREG DIN 908 metric flat head socket pipe plugs are manufactured from A4 marine stainless steel (SUS316) to Grade A4-70, with a whitened and passivated surface finish. The addition of molybdenum (2–3%) in SUS316 provides significantly enhanced resistance to chloride-induced pitting and crevice corrosion compared to A2 (SUS304) — making these plugs the preferred choice for marine, offshore, coastal, chemical processing, and food-grade applications where long-term corrosion resistance is critical.

The flat (parallel) metric thread combined with the flat sealing face requires a copper or aluminium sealing washer (not included) to achieve a pressure-tight seal. The internal hexagon (Allen key) drive allows installation and removal in recessed or confined spaces.

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Product Specifications

Standard	DIN 908
Thread Type	Metric straight (parallel) thread per ISO 261 / DIN 13
Head Type	Flat head (flush) with internal hexagon (Allen key) drive
Sealing Method	Flat face — requires copper or aluminium sealing washer (DIN 7603)
Material	A4 Marine Stainless Steel / SUS316 / 1.4401
Grade	A4-70
Surface Finish	Whitened & Passivated
Size Range	M10 × 1 — M52 × 2
Drive Tool	Internal hexagon (Allen key) per ISO 2936
Key Advantage vs A2	Superior chloride & pitting corrosion resistance due to 2–3% Mo content

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Product Gallery

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Dimensional Data — DIN 908 Metric Socket Pipe Plugs

All dimensions in millimeters (mm). Data per DIN 908 standard.

Thread (d)	Pitch (mm)	s — A/F (mm)	e — A/C (mm)	k — Head Height (mm)	t — Socket Depth (mm)	Sealing Ø (mm)
M10	1.0	17	19.6	4	3	10
M12	1.5	19	21.9	5	4	12
M14	1.5	22	25.4	5	4	14
M16	1.5	24	27.7	6	5	16
M18	1.5	27	31.2	6	5	18
M20	1.5	30	34.6	7	6	20
M22	1.5	32	36.9	7	6	22
M24	2.0	36	41.6	8	6	24
M26	1.5	36	41.6	8	6	26
M27	2.0	41	47.3	8	6	27
M30	2.0	46	53.1	9	8	30
M33	2.0	50	57.7	10	8	33
M36	2.0	55	63.5	10	8	36
M38	1.5	55	63.5	10	8	38
M42	2.0	65	75.1	12	10	42
M45	2.0	70	80.8	12	10	45
M48	2.0	75	86.6	14	12	48
M52	2.0	80	92.4	14	12	52

* s = across flats (A/F); e = across corners (A/C); k = head height; t = minimum socket depth. All dimensions per DIN 908.

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Allen Key (Hex Key) Size Reference

Thread	M10	M12	M14	M16	M18	M20	M22	M24	M27	M30	M33	M36	M42	M48	M52
Hex Key (mm)	14	17	19	22	24	27	30	32	36	41	46	50	55	65	70

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Material & Grade Properties

Property	Value
Material Designation	A4 / SUS316 / 1.4401 / 0Cr17Ni12Mo2
Property Class	A4-70
Tensile Strength (Rm)	≥ 700 MPa
0.2% Proof Stress (Rp0.2)	≥ 450 MPa
Hardness	≤ 250 HV
Molybdenum Content	2.0 – 3.0% — key differentiator vs A2 (SUS304)
Corrosion Resistance	Excellent — superior chloride, pitting & crevice corrosion resistance vs A2
Magnetic	Slightly magnetic after cold working
Surface Finish	Whitened & Passivated
Temperature Range	−50°C to +300°C (continuous service)

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A4 (SUS316) vs A2 (SUS304) — Why Choose Marine Grade?

Property	A4 — SUS316 (This Product)	A2 — SUS304
Molybdenum	2–3% Mo — present	None
Chloride resistance	Excellent — resists seawater, de-icing salts, chlorinated water	Good — may pit in high-chloride environments
Pitting resistance (PREN)	~24–26	~18–20
Crevice corrosion	Significantly better	Susceptible in chloride environments
Acid resistance	Better in reducing acids (e.g. H₂SO₄)	Good in oxidising acids
Food & pharma	Preferred grade for food contact & pharmaceutical	Acceptable for many food applications
Cost	Higher (Mo content)	Lower
Recommended for	Marine, offshore, coastal, chemical, food, pharma	General outdoor, mild industrial

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Sealing & Installation Notes

• Thread type: Metric straight (parallel) — does NOT self-seal. A sealing washer is mandatory for pressure-tight installation.
• Recommended sealing washer: Copper (DIN 7603 Form A) or aluminium sealing washer — sized to match thread diameter. For marine/chemical environments, consider PTFE-coated or stainless-compatible washers.
• Torque: Apply recommended torque per thread size. Over-torquing may damage the sealing face or thread.
• Re-use: Replace sealing washer on each re-installation to ensure leak-free seal.
Galvanic compatibility: A4 stainless is compatible with most stainless steel and titanium components. Avoid direct contact with carbon steel in wet environments.
• Drive tool: Use a correctly sized, high-quality hex key or hex bit socket. Worn or undersized keys risk rounding the socket.

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Typical Applications

• 🚢 Marine & offshore — sealing hydraulic and fluid ports on vessels, offshore platforms, and marine equipment
• 🌊 Coastal & saltwater environments — where A2 stainless would be susceptible to chloride pitting
• 🧪 Chemical processing — sealing ports in chemical plant equipment exposed to chlorides or mild acids
• 🍼 Food & beverage / pharmaceutical — hygienic port closures in food-grade and pharma processing equipment
• 🔧 Hydraulic systems — sealing unused ports on manifolds, cylinders, and valve blocks in marine environments
• 🏭 Industrial machinery — oil and fluid circuit port closures where superior corrosion resistance is specified

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Frequently Asked Questions

Q: Why choose A4 (SUS316) over A2 (SUS304) for pipe plugs?
A: A4 contains 2–3% molybdenum which dramatically improves resistance to chloride-induced pitting and crevice corrosion. In marine, coastal, or chemical environments where A2 may corrode, A4 provides reliable long-term performance.

Q: Does DIN 908 A4 require a sealing washer?
A: Yes. DIN 908 uses a straight (parallel) metric thread with a flat sealing face — it does not self-seal. A copper or aluminium sealing washer (DIN 7603) must be used to achieve a pressure-tight seal.

Q: Is A4 stainless suitable for seawater immersion?
A: A4 (SUS316) performs significantly better than A2 in seawater and high-chloride environments. However, for continuous seawater immersion under crevice conditions, consult a corrosion engineer. Duplex 2205 may be specified for the most demanding offshore applications.

Q: What Allen key size do I need?
A: The hex key size equals the across-flats (s) dimension. For example: M16 → 22mm hex key, M20 → 27mm, M24 → 32mm. See the Allen Key Size Reference table above.

Q: Can I use PTFE tape instead of a sealing washer?
A: PTFE tape is not recommended as the primary sealant for DIN 908 metric straight thread. Use a proper copper or aluminium sealing washer (DIN 7603) for a reliable, pressure-rated seal.