Home » GB9074.4-1988 Phillips Pan Head SEMS Screws - Marine Stainless Steel (A4)

GB9074.4-1988 Phillips Pan Head SEMS Screws - Marine Stainless Steel (A4)

GB9074.4-1988 Phillips Pan Head SEMS Screws – Marine Stainless Steel A4 (SUS316) – A4-70

FULLERKREG supplies GB9074.4-1988 Phillips pan head SEMS screws manufactured from marine-grade austenitic stainless steel A4 (SUS316 / 316 / 18-10-Mo), with a bright-pickled and passivated surface finish. Each screw ships with a pre-assembled flat washer (GB9074.24) and a spring washer (GB9074.26), permanently captivated on the shank — delivering the highest level of corrosion resistance available in the GB9074.4 SEMS screw range, with zero loose washer handling on the assembly line.

What are Phillips Pan Head SEMS Screws?

SEMS screws (also called combination screws or pre-assembled screws) are fasteners in which one or more washers are permanently captured on the screw shank before threading. The washer(s) are assembled onto the blank shank and then the thread is rolled, making the outer diameter of the thread larger than the inner diameter of the washer — so the washer can never fall off during handling or installation.

GB9074.4-1988 defines the Chinese national standard for cross-recessed (Phillips) pan head combination screws with pre-assembled spring washer and plain washer. The assembly is expressed as:

GB9074.4 = GB818 (Pan Head Screw) + GB9074.24 (Plain Washer) + GB9074.26 (Spring Washer)

The pan head profile provides a broad, low-profile bearing surface for excellent load distribution. The Phillips (cross-recessed) drive enables fast, reliable torquing with standard power tools and is well-suited to both manual and automated assembly environments.

Benefits of Using Phillips Pan Head SEMS Screws in A4 Stainless Steel

  • Eliminates loose washer handling — washers are permanently captivated; no separate picking, placing, or alignment required during assembly.
  • Faster assembly — one part replaces three; dramatically reduces cycle time in high-volume or field assembly operations.
  • Reduced risk of missing washers — captive design prevents washer omission errors that can cause field failures or warranty claims.
  • Superior chloride corrosion resistance — the 2–3% molybdenum content in SUS316 dramatically improves resistance to chloride-induced pitting and crevice corrosion compared to A2 (SUS304), making A4 the preferred choice for marine, coastal, and chemical environments.
  • Excellent resistance to acids & chemicals — SUS316 resists a wide range of acids, alkalis, and industrial chemicals including sulfuric acid, phosphoric acid, and chloride-containing cleaning agents.
  • Non-magnetic & hygienic — austenitic stainless steel is non-magnetic and easy to clean, suitable for food processing, pharmaceutical, and medical applications.
  • No coating required — corrosion resistance is inherent to the alloy; no risk of coating delamination, flaking, or plating failure in service.
  • Space-saving installation — the shortened unthreaded shank allows clamping of thinner panels; minimum clampable thickness is approximately half that of standard combination screws.
  • Anti-loosening — the pre-assembled spring washer provides continuous axial load to resist vibration-induced loosening in service.
  • Suitable for automated feeding — consistent geometry and captive washers make these screws ideal for vibratory bowl feeders and robotic assembly systems.

Material & Finish

Component Material Steel Grade Surface Treatment Strength Grade
Screw Body Marine Stainless Steel A4 (SUS316 / 18-10-Mo) AISI 316 Bright Pickled & Passivated A4-70
Plain Washer (Flat) Stainless Steel A4 (SUS316) AISI 316 Bright Pickled & Passivated —
Spring Washer Stainless Steel A4 (SUS316) AISI 316 Bright Pickled & Passivated —

A4-70 denotes marine-grade austenitic stainless steel (A4) with a minimum tensile strength of 700 MPa. The molybdenum addition (2–3%) is the critical differentiator from A2 (SUS304), providing significantly enhanced resistance to pitting and crevice corrosion in chloride-rich environments such as seawater, de-icing salts, and industrial process fluids.

Key mechanical properties (A4-70):

  • Tensile strength: ≥ 700 MPa
  • 0.2% proof stress: ≥ 450 MPa
  • Elongation: ≥ 20%
  • Hardness: ≤ 220 HV

Chemical composition highlights (SUS316 / AISI 316):

  • Chromium (Cr): 16.0 – 18.0%
  • Nickel (Ni): 10.0 – 14.0%
  • Molybdenum (Mo): 2.0 – 3.0% — key to superior chloride resistance
  • Carbon (C): ≤ 0.08%

Typical salt-spray resistance: ≥ 500 hours to red rust — significantly exceeding A2 stainless (≥ 200 h) and zinc-plated steel (≥ 48–72 h).

Dimensional Data – GB9074.4-1988 Phillips Pan Head SEMS Screws

Thread range: M3 – M8  |  Length range: 5 mm – 50 mm  |  Drive: Phillips (Cross Recessed, Type H)

Thread (d) Pitch (mm) Head Dia. dk (mm) Head Height k (mm) Drive No. Min. Clamp Thickness (mm) Max. Clamp Thickness (mm) Unit Weight (g/100 pcs)*
M3 0.5 5.6 2.0 PH1 0.5 varies by length ~41
M4 0.7 8.0 2.6 PH2 0.6 varies by length ~102
M5 0.8 9.5 3.3 PH2 0.8 varies by length ~198
M6 1.0 12.0 3.9 PH3 1.0 varies by length ~340
M8 1.25 16.0 5.0 PH4 1.2 varies by length ~800

* Unit weight is approximate for a representative length (e.g., 16 mm). SUS316 density ~7.98 g/cm³. Actual weight varies by length. Contact FULLERKREG for exact weight data per SKU.

Dimensions of Pre-Assembled Washers

The flat washer conforms to GB9074.24 dimensions. The spring washer conforms to GB9074.26. All washer components are stainless steel A4 (SUS316), fully matched to the screw body material for complete galvanic compatibility and uniform corrosion resistance throughout the assembly. Both washers are permanently captivated on the screw shank prior to shipment.

Flat Washer Dimensions (GB9074.24)

Thread (d) Inner Dia. d1 (mm) Outer Dia. d2 (mm) Thickness h (mm)
M3 3.2 6.0 0.5
M4 4.3 8.0 0.8
M5 5.3 9.0 1.0
M6 6.4 11.0 1.6
M8 8.4 15.0 1.6

Note: GB9074.24 plain washer outer diameters are optimized for the SEMS captive assembly process and are slightly smaller than DIN 125A equivalents.

Spring Washer Dimensions (GB9074.26)

Thread (d) Inner Dia. d1 (mm) Outer Dia. d2 (mm) Thickness s (mm) Height h (mm)
M3 3.1 5.1 0.8 1.6
M4 4.1 6.8 0.9 1.8
M5 5.1 8.2 1.2 2.4
M6 6.1 9.9 1.6 3.2
M8 8.1 13.0 2.0 4.0

Product Images

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Applications

GB9074.4-1988 Phillips pan head SEMS screws in marine stainless steel A4 (SUS316) / A4-70 are the premium choice for the most demanding corrosion environments:

  • Marine & offshore equipment — boat fittings, deck hardware, offshore platform structures, and subsea equipment housings where continuous seawater exposure demands the highest corrosion resistance
  • Coastal & waterfront architecture — façade panels, handrails, signage, and structural fixings in salt-laden coastal atmospheres
  • Chemical & petrochemical plant — process equipment, pipework supports, and instrument enclosures exposed to chlorides, acids, and aggressive industrial chemicals
  • Food & beverage processing — SUS316 is the industry standard for food contact surfaces; ideal for processing machinery, conveyors, and packaging equipment subject to frequent washdown with chlorinated cleaning agents
  • Pharmaceutical & biotech equipment — cleanroom-compatible, non-magnetic, and resistant to sterilization chemicals including steam, hydrogen peroxide, and chlorine-based disinfectants
  • Swimming pool & water treatment — resistance to chlorinated water and pool chemicals that rapidly corrode A2 stainless and zinc-plated fasteners
  • Medical devices & surgical equipment — biocompatible, autoclavable, and non-magnetic; suitable for medical instrument assembly and surgical equipment housings
  • Desalination & water treatment plant — resistance to high-chloride process streams and brine environments

A4 vs A2 — when to upgrade: If your application involves direct seawater contact, chlorinated water, de-icing salts, or aggressive chemical cleaning agents, A4 (SUS316) is strongly recommended over A2 (SUS304). The molybdenum content in A4 provides a critical barrier against pitting corrosion that A2 cannot match in these environments.

Why FULLERKREG?

  • 🏭 Direct manufacturer — full control over SUS316 material sourcing, cold forming, and passivation treatment
  • 📐 Standard-compliant — manufactured and inspected to GB9074.4-1988 with full dimensional and material traceability
  • ✅ Material certification — mill test certificates (MTC) with chemical composition and mechanical properties for SUS316 / A4 available on request
  • 🌍 Global supply — export packaging, English documentation, and worldwide logistics support
  • 📦 Bulk & wholesale ready — available in bulk bags, boxes, or custom packaging for OEM and MRO customers
  • 🔬 Quality assured — incoming material certification, hardness testing, and salt-spray testing (≥ 500 h) available on request
  • 💬 Engineering support — custom sizes, SUS316L (low carbon) options, and special specifications available; contact our technical team

For custom specifications, SUS316L options, non-standard sizes, or volume pricing, please contact the FULLERKREG team directly.

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