Home » Imperial BSPP Flat Head Socket Pipe Plugs (DIN 908) — Marine Stainless Steel A4 (SUS316)

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

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

FULLERKREG DIN 908 imperial BSPP 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 definitive choice for marine, offshore, coastal, chemical processing, and food-pharmaceutical applications where long-term corrosion resistance in aggressive environments is critical.

These plugs feature British Standard Pipe Parallel (BSPP / G thread) — the straight parallel pipe thread dominant in hydraulic and pneumatic systems across the UK, Europe, Asia, and Commonwealth markets. A bonded seal (Dowty washer) or O-ring face seal is required to achieve a pressure-tight connection. The internal hexagon (Allen key) drive allows installation in recessed or confined port locations.

Product Specifications

Standard DIN 908 (Imperial Pipe Thread — BSPP, Flat Head)
Thread Type BSPP — British Standard Pipe Parallel (G thread) per ISO 228-1 / BS EN ISO 228
Thread Profile Whitworth 55° thread form, parallel (straight) — does NOT self-seal
Head Type Flat head (flush) with internal hexagon (Allen key) drive
Sealing Method Flat face — requires bonded seal (Dowty washer) or O-ring face seal
Material A4 Marine Stainless Steel / SUS316 / 1.4401
Grade A4-70
Surface Finish Whitened & Passivated
Size Range G1/8 — G2 (BSPP)
Drive Tool Internal hexagon (Allen key) per ISO 2936
Key Advantage vs A2 Superior chloride & pitting corrosion resistance due to 2–3% Mo content — preferred for seawater, offshore & chemical environments

Product Gallery

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Dimensional Data — DIN 908 BSPP Flat Head Socket Pipe Plugs

All dimensions in millimeters (mm) unless noted. Thread sizes in BSP (G) designation. Data per DIN 908 standard / ISO 228-1.

Thread (G) TPI Thread Ø (mm) s — A/F (mm) e — A/C (mm) k — Head Height (mm) t — Socket Depth (mm) Sealing Ø (mm)
G 1/8 28 9.728 14 16.2 4 3 10
G 1/4 19 13.157 19 21.9 5 4 14
G 3/8 19 16.662 22 25.4 5 4 17
G 1/2 14 20.955 27 31.2 6 5 21
G 5/8 14 22.911 30 34.6 6 5 23
G 3/4 14 26.441 32 36.9 7 6 27
G 7/8 14 30.201 36 41.6 7 6 30
G 1 11 33.249 41 47.3 8 6 33
G 1 1/8 11 37.897 46 53.1 8 6 38
G 1 1/4 11 41.910 50 57.7 9 8 42
G 1 1/2 11 47.803 55 63.5 10 8 48
G 1 3/4 11 53.746 60 69.3 10 8 54
G 2 11 59.614 65 75.1 12 10 60

* s = across flats (A/F); e = across corners (A/C); k = head height; t = minimum socket depth; TPI = threads per inch. All dimensions per DIN 908 / ISO 228-1.

Allen Key (Hex Key) Size Reference

Thread G1/8 G1/4 G3/8 G1/2 G3/4 G1 G1¼ G1½ G2
Hex Key (mm) 12 17 19 24 30 36 46 50 60

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)
Pitting Resistance (PREN) ~24–26 (vs ~18–20 for A2)
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)

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

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
Marine / offshore ✅ Preferred grade ⚠️ Marginal — may corrode in direct seawater exposure
Food & pharma ✅ Preferred grade for food contact & pharmaceutical ✅ Acceptable for many food applications
Chemical processing ✅ Better in reducing acids & chloride-containing media ✅ Good in oxidising acids
Cost Higher (Mo content) Lower

Sealing & Installation Notes

  • Thread type: BSPP (G thread) is a parallel thread — it does NOT self-seal. A bonded seal (Dowty washer) or O-ring face seal is mandatory for pressure-tight installation.
  • Recommended sealant: Bonded seal (Dowty washer) with stainless outer ring and NBR or Viton rubber, sized to match thread designation. For aggressive chemical or high-temperature media, specify Viton (FKM) rubber bonded seals.
  • Do NOT use PTFE tape: PTFE tape is designed for tapered threads (BSPT/NPT) and is not effective as a primary sealant for BSPP parallel threads.
  • Port compatibility: BSPP (G) plugs fit BSPP-tapped ports only. Do NOT install in BSPT (R thread) tapered ports.
  • Anti-galling: Apply a small amount of anti-seize compound (nickel-based recommended for marine environments) to threads before installation to prevent galling on stainless-to-stainless connections.
  • Galvanic compatibility: A4 stainless is compatible with most stainless steel, titanium, and aluminium components. Avoid direct contact with carbon steel in seawater or high-chloride environments.
  • Re-use: Replace bonded seal on each re-installation. A4 stainless plugs can be re-used many times in service — inspect threads and sealing face for damage before re-installation.

Typical Applications

  • 🚢 Marine & offshore — sealing BSPP ports in hydraulic and fluid systems on vessels, offshore platforms, and marine equipment where A2 would be insufficient
  • 🌊 Coastal & saltwater environments — hydraulic and pneumatic port closures exposed to salt spray or chloride-laden air
  • 🧪 Chemical processing — sealing BSPP ports in chemical plant equipment exposed to chlorides, mild acids, or aggressive media
  • 🍼 Food & beverage / pharmaceutical — hygienic BSPP port closures in food-grade and pharma processing equipment — A4 is the preferred grade for direct food contact
  • 🔧 Hydraulic systems in corrosive environments — sealing unused BSPP ports on manifolds and valve blocks in marine, chemical, or wash-down environments
  • 🏭 Industrial machinery — fluid circuit port closures where superior corrosion resistance over A2 is specified by the OEM or end user

Frequently Asked Questions

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

Q: Does BSPP (G thread) self-seal?
A: No. BSPP is a parallel (straight) thread — it does not self-seal through thread interference. A bonded seal (Dowty washer) or O-ring face seal must be used. Do not use PTFE tape as a primary sealant for BSPP connections.

Q: Can stainless steel threads gall (seize) in marine environments?
A: Yes. Stainless steel is susceptible to galling (cold welding / thread seizure) when torqued against stainless ports without lubrication. In marine environments, use a nickel-based anti-seize compound on threads before installation. This is especially important for larger thread sizes (G3/4 and above).

Q: Is A4 stainless suitable for continuous seawater immersion?
A: A4 (SUS316) performs significantly better than A2 in seawater and high-chloride environments. For most marine hydraulic port sealing applications, A4 provides excellent long-term performance. For continuous seawater immersion under crevice conditions (e.g. submerged fittings), consult a corrosion engineer — Duplex 2205 may be specified for the most demanding offshore applications.

Q: What bonded seal material should I use with A4 stainless plugs in marine service?
A: For marine and offshore applications, specify bonded seals with a stainless steel outer ring and Viton (FKM) rubber — Viton provides superior resistance to seawater, hydraulic fluids, and elevated temperatures compared to standard NBR rubber bonded seals.

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