Square Head Bolt A4-70 Anti-Rotation Marine Machine Bolt
Square Head Bolt A4-70 — Anti-Rotation Marine Machine Bolt
Thesquare head bolt — also called a square head machine boltoranti-rotation bolt — features a square-section head that seats into a matching square recess in the mating surface, preventing the bolt from rotating during nut tightening. This eliminates the need to hold the bolt head with a wrench from the opposite side, making it ideal for applications where only one side of the joint is accessible, or where the bolt must remain fixed in a slot, channel, or keyed hole.
In marine and industrial installations, square head bolts are valued for three specific advantages: anti-rotation — the square head locks into a square hole or T-slot, preventing the bolt from spinning during assembly; single-side assembly — the bolt can be inserted from a concealed slot and held in position while the nut is tightened from the accessible side; and sliding adjustment — when mounted in a T-slot or channel, the square head allows the bolt to slide along the slot for position adjustment before final clamping.
Square Head vs Hex Head — When to Specify Square
| Feature | Square Head Bolt | Hex Head Bolt |
|---|---|---|
| Anti-rotation capability | Yes — locks into square recess or slot | No — requires wrench to hold head |
| Single-side assembly | Yes — bolt seats and holds in slot | No — wrench required on both sides |
| T-slot / channel compatibility | Excellent — slides along slot | Not suitable |
| Wrenching torque capacity | Lower (smaller head flats) | Higher (6 flats = more torque) |
| Typical use case | T-slot, pipe clamp, fixture, channel mount | General structural and flange bolting |
Marine and Industrial Applications
- Pipe clamp and strut channel mounting: Square head bolts slide along the channel slot to the desired position, then the nut is tightened from the accessible side to clamp the pipe. This is the standard fastening method for cable tray support, pipe hanger, and instrument rack assemblies.
- Woodworking and composite fixture: In marine workshop jigs and assembly fixtures, square head bolts seat in T-slot table grooves and can be repositioned without removing the bolt — essential for adjustable workholding.
- Old machinery maintenance: Many legacy machines (pumps, compressors, gearboxes built before 1980) use square head set screws and bolts as original fasteners. Replacement square head bolts in A4-70 stainless restore corrosion resistance without modifying the original threaded holes.
- Deck equipment base adjustment: Where equipment bases have slotted mounting holes, square head bolts allow fore-aft position adjustment before final clamping — useful for alignment of navigation equipment, radar pedestals, and winch bases.
- Grating and tread plate fastening: Square head bolts seat into square holes punched in grating panels, preventing rotation during installation from the top side only.
Technical Standards
| Standard | Scope |
|---|---|
| DIN 15 | Square head bolts with square neck — German national standard (withdrawn, still widely referenced in European marine specifications) |
| ASME B18.2.2 | Square and hex nuts — includes square head bolt dimensional data for inch-series fasteners (US market) |
| BS 4933 | Square head set screws for general engineering (UK market) |
| ISO 898-1 | Mechanical properties — property classes for carbon steel bolts (Grade 4.8–10.9) |
| ISO 3506-1 | Mechanical properties of stainless steel fasteners — A2-70, A4-70, A4-80 |
Material and Finish Options
| Grade | Material | Tensile Strength | Recommended Environment |
|---|---|---|---|
| A4-70 | AISI 316 Stainless Steel | 700 MPa | Seawater exposure, salt spray, bilge area |
| A4-80 | AISI 316 Cold-Worked | 800 MPa | Same as A4-70 with higher tensile strength |
| A2-70 | AISI 304 Stainless Steel | 700 MPa | Freshwater, indoor, non-corrosive zone |
| Grade 8.8 | Carbon Steel, quenched & tempered | 800 MPa | Protected environment, HDG or Dacromet coated |
Recommendation: For marine deck and engine room applications where the bolt head is exposed to salt spray or bilge moisture, specify A4-70 as minimum. For indoor machinery spaces or freshwater cooling systems, A2-70 is sufficient. Grade 8.8 carbon steel with HDG coating is suitable for non-corrosive industrial mounting.
Product Specification
| Item | Detail |
|---|---|
| Product Name | Square Head Bolt / Anti-Rotation Machine Bolt |
| Standard Reference | DIN 15 / ASME B18.2.2 (dimensional) |
| Head Type | Square head (with or without square neck) |
| Size Range | M6 – M36 |
| Length | 20 mm – 500 mm (standard); custom on request |
| Thread | Metric coarse, full-thread / partial-thread |
| Material — Stainless | A2-70 / A4-70 / A4-80 |
| Material — Carbon Steel | Grade 4.8 / 8.8 / 10.9 (per ISO 898-1) |
| Surface Finish — SS | Passivated after forming |
| Surface Finish — Carbon Steel | HDG / Zinc plated / Dacromet / Geomet / Black oxide |
| Certification | EN 10204 3.1 material certificate; third-party inspection available |
| Packing | Carton / Pallet / Custom labeling |
FAQ
Q1: Why use a square head bolt instead of a hex bolt?
A: Square head bolts are specified when anti-rotation is required — the square head locks into a matching square hole, T-slot, or channel without needing a wrench on the head side. This enables single-side assembly and allows position adjustment in slotted mounting holes. Hex bolts require wrench access on both sides.
Q2: What is the difference between a square head bolt and a square head set screw?
A: A square head bolt has a machine thread and is used with a nut to clamp two or more components together. A square head set screw (also called a grub screw) is fully threaded and is used to secure a rotating component (gear, pulley, coupling) onto a shaft by pressing against the shaft surface. Both share the square head geometry for anti-rotation, but serve different joint functions.
Q3: Can you supply square head bolts in A4-70 stainless steel for seawater exposure?
A: Yes. A4-70 (AISI 316) is our recommended grade for marine deck and engine room applications where the bolt head is exposed to salt spray or bilge moisture. For higher tensile strength with the same corrosion resistance, A4-80 is also available.
Q4: What sizes do you manufacture?
A: Standard range is M6 to M36 in lengths from 20 mm to 500 mm. For sizes outside this range or non-standard head dimensions, we manufacture to customer drawings. Send us the drawing with head size, thread specification, material grade, and quantity.
Contact
Email:sales@sinofastener.com
Web:www.sinofastener.com
SINOFASTENER — Your Reliable Marine Fastener Partner
