Home » Metric Hexagon Socket Screw Plug with Collar MF (DIN 908) — Carbon Steel, Black Oxide

Metric Hexagon Socket Screw Plug with Collar MF (DIN 908) — Carbon Steel, Black Oxide

Metric Hexagon Socket Screw Plug with Collar MF — DIN 908 — Carbon Steel, Black Oxide

FULLERKREG DIN 908 MF metric fine thread hexagon socket screw plugs with collar are manufactured from 35K carbon steel to Grade 6.8, with a black oxide surface finish. The integrated collar (flange) beneath the hex socket head provides a wider sealing bearing surface and acts as a positive stop — ensuring consistent seating depth and improved sealing reliability compared to standard collarless plugs.

The metric fine (MF) thread offers finer pitch than standard metric coarse, providing greater resistance to vibration loosening and more precise torque control — making these plugs the preferred choice for hydraulic manifolds, machine tool coolant circuits, and precision fluid power systems. The internal hexagon (Allen key) drive allows installation in recessed or confined port locations.

Product Specifications

Standard DIN 908 (MF — Metric Fine Thread with Collar)
Thread Type Metric fine (MF) straight thread per ISO 261 / DIN 13
Head Type Flat head with collar (flange) and internal hexagon (Allen key) drive
Collar Function Wider sealing face, positive stop, consistent seating depth
Sealing Method Collar face — requires copper or aluminium sealing washer (DIN 7603) or bonded seal
Material Carbon Steel 35K
Grade 6.8
Surface Finish Black Oxide (Blackened)
Size Range M10 × 1 — M52 × 2 (fine pitch)
Drive Tool Internal hexagon (Allen key) per ISO 2936
Key Advantage Fine thread + collar = superior vibration resistance & sealing reliability

Product Gallery

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Dimensional Data — DIN 908 MF Socket Screw Plugs with Collar

All dimensions in millimeters (mm). MF = Metric Fine thread. Data per DIN 908 standard and ASPEN specification sheet.

Thread (d) Pitch (mm) s — A/F (mm) e — A/C (mm) k — Head Height (mm) t — Socket Depth (mm) D — Collar Ø (mm) Sealing Ø (mm)
M10 1.0 17 19.6 4 3 16 10
M12 1.5 19 21.9 5 4 18 12
M14 1.5 22 25.4 5 4 20 14
M16 1.5 24 27.7 6 5 22 16
M18 1.5 27 31.2 6 5 25 18
M20 1.5 30 34.6 7 6 28 20
M22 1.5 32 36.9 7 6 30 22
M24 2.0 36 41.6 8 6 34 24
M26 1.5 36 41.6 8 6 34 26
M27 2.0 41 47.3 8 6 38 27
M30 2.0 46 53.1 9 8 42 30
M33 2.0 50 57.7 10 8 46 33
M36 2.0 55 63.5 10 8 50 36
M38 1.5 55 63.5 10 8 52 38
M42 2.0 65 75.1 12 10 60 42
M45 2.0 70 80.8 12 10 64 45
M48 2.0 75 86.6 14 12 68 48
M52 2.0 80 92.4 14 12 72 52

* s = across flats (A/F); e = across corners (A/C); k = head height; t = minimum socket depth; D = collar outer diameter. MF = metric fine thread. All dimensions per DIN 908. Verify against current standard for safety-critical applications.

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

Material & Grade Properties

Property Value
Material Carbon Steel 35K (medium carbon steel)
Property Class Grade 6.8
Tensile Strength (Rm) ≥ 600 MPa
0.2% Proof Stress (Rp0.2) ≥ 480 MPa
Hardness 190 – 250 HV
Surface Finish Black Oxide (Blackened) — mild corrosion protection, oil-retentive surface
Black Oxide Thickness 1–2 μm (does not affect thread tolerances)
Corrosion Resistance Mild — suitable for indoor, oil-wetted, or protected environments. Apply oil or grease for enhanced protection.
Temperature Range −30°C to +150°C (black oxide service limit)
Magnetic Yes

MF Fine Thread vs Standard Metric Coarse — Why Fine Thread?

Feature MF Fine Thread (This Product) Standard Metric Coarse
Pitch Finer (e.g. M20×1.5 vs M20×2.5) Coarser standard pitch
Vibration resistance Superior — smaller helix angle resists self-loosening Standard
Torque control More precise — finer adjustment per turn Standard
Thread engagement More threads per unit length — higher pull-out strength in thin walls Fewer threads per unit length
Typical use Hydraulic manifolds, precision machine tools, high-vibration environments General industrial, structural
Port compatibility Must match MF-tapped port — not interchangeable with coarse thread ports Standard metric ports

Collar (Flange) — Key Advantages

  • Wider sealing face: The collar provides a larger contact area for the sealing washer — reducing unit pressure on the washer and improving seal reliability.
  • Positive stop: The collar acts as a mechanical stop, preventing over-insertion and ensuring consistent seating depth across all installations.
  • No separate washer flange needed: The collar integrates the washer bearing surface into the plug body — simplifying assembly.
  • Easier alignment: The collar helps centre the plug in the port during installation, reducing cross-threading risk.

Sealing & Installation Notes

  • Thread type: Metric fine straight thread — does NOT self-seal. A sealing washer or bonded seal (Dowty seal) is required for pressure-tight installation.
  • Recommended sealant: Copper or aluminium sealing washer (DIN 7603) sized to thread diameter, or bonded seal (Dowty washer) for higher-pressure hydraulic applications.
  • Port compatibility: MF fine thread — ensure the mating port is tapped to the same fine pitch. Do NOT install in standard metric coarse-tapped ports.
  • Black oxide & corrosion: Black oxide provides only mild corrosion protection. Apply hydraulic oil or anti-corrosion grease to threads and sealing face before installation in humid or outdoor environments.
  • Torque: Apply recommended torque per thread size. The collar provides a positive stop — do not over-torque beyond collar contact.
  • Re-use: Replace sealing washer on each re-installation. Inspect black oxide surface for rust before re-use in critical applications.
  • Drive tool: Use a correctly sized, high-quality hex key or hex bit socket. Worn or undersized keys risk rounding the socket.

Typical Applications

  • 🔧 Hydraulic manifolds & valve blocks — sealing unused MF-tapped ports in hydraulic systems where vibration resistance is critical
  • ⚙️ Machine tools & CNC equipment — sealing coolant and lubrication circuit ports in high-vibration machining environments
  • 🚗 Automotive & industrial machinery — oil and fluid circuit port closures in engine blocks, gearboxes, and hydraulic units
  • 💨 Pneumatic systems — closing unused ports in pneumatic valve manifolds with fine-thread ports
  • 🏭 Industrial equipment — general fluid sealing in carbon steel environments where stainless is not required

Frequently Asked Questions

Q: What does MF mean in DIN 908 MF?
A: MF stands for Metric Fine — indicating that the thread pitch is finer than standard metric coarse (MC). For example, M20 MF uses a 1.5mm pitch vs 2.5mm for standard M20 coarse. Fine thread provides better vibration resistance and more precise torque control.

Q: What is the purpose of the collar on this plug?
A: The collar (flange) provides a wider sealing bearing surface for the sealing washer, acts as a positive mechanical stop to ensure consistent seating depth, and helps centre the plug during installation. It improves sealing reliability compared to collarless plugs.

Q: Does this plug require a sealing washer?
A: Yes. DIN 908 MF uses a straight (parallel) metric fine thread with a flat collar face — it does not self-seal. A copper or aluminium sealing washer (DIN 7603) or bonded seal (Dowty washer) must be used for a pressure-tight seal.

Q: Can I use this plug in a standard metric coarse-tapped port?
A: No. MF fine thread is NOT interchangeable with standard metric coarse thread. Always verify the thread pitch of the mating port before ordering. Installing a fine-thread plug in a coarse-tapped port will result in cross-threading and damage.

Q: Does black oxide provide corrosion protection?
A: Black oxide provides only mild corrosion protection — it is primarily a decorative and oil-retentive finish. For outdoor or humid environments, apply hydraulic oil or anti-corrosion grease to the plug before installation. For corrosive environments, specify stainless steel grades instead.

Q: What is Grade 6.8 carbon steel?
A: Grade 6.8 indicates a tensile strength of ≥600 MPa and proof stress of ≥480 MPa per ISO 898-1. The 35K carbon steel base material provides good machinability and adequate strength for hydraulic port sealing applications at standard working pressures.

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