Square Head Bolts (DIN 478 / DIN 479 / ANSI B18.2.1)
Modern hex bolts often fail in environments with heavy debris or limited visibility. Square Head Bolts offer a superior solution for these “blind” applications. The broad four-sided geometry allows for easy engagement with an open-ended wrench or adjustable spanner without the precision alignment required by hex heads. Whether specifically designed with a Collar (DIN 478) to protect soft castings or a Dog Point (DIN 479) for shaft alignment, our bolts ensure high torque transmission without cam-out, making them the standard for heavy machinery, railway infrastructure, and heritage restoration.
- Zero-slip wrench engagement
- High torque transmission
- Ideal for blind spots
- Collar options prevent embedment
- Dog point aids alignment
- Available in Grade 8.8 / 316SS
Technical Specifications
Product Name
Square Head Bolts (Machine Bolts / Set Screws)
Standards
DIN 478 (with Collar), DIN 479 (Short Dog Point), ANSI B18.2.1
Material
Carbon Steel (C1045), Alloy Steel (SCM435), Stainless Steel A2/A4
Diameter Range
M6 – M36 (1/4″ – 1-1/2″)
Grades
Class 4.8, 5.8, 8.8, 10.9; Imperial Grade 2, 5, 8
Surface Finish
Black Oxide, Zinc Plated (Cr3+), HDG, Geomet 500
Certifications
ISO 9001:2015, EN 10204 3.1, RoHS Compliant
1: Slippage and “Rounding Off” in Dirty Environments.
The Reality: In agricultural or mining equipment covered in grease/mud, 6-point hex heads are hard to grip. Operators often “round off” the corners when the wrench slips.
The Solution: The Square Head design offers a massive 90° engagement angle. Even with worn tools or debris-covered heads, the wrench finds a solid purchase, allowing for safe high-torque tightening.
2: Damage to Soft Cast Iron or Aluminum Surfaces.
The Reality: Standard bolts have a small bearing area. Under high load, the head digs into softer housing materials (embedment), causing loss of preload.
The Solution: Our DIN 478 (Square Head with Collar) features an integrated flange. This increases the bearing area, reducing surface pressure (Psi) and protecting the mating surface without needing a separate washer.
3: Misalignment in Automated Assembly.
The Reality: Starting a bolt into a threaded hole blindly often leads to cross-threading, destroying expensive castings.
The Solution: The DIN 479 (Dog Point) features an unthreaded pilot tip. It locates the hole before threads engage, ensuring perfect alignment every time.
Comprehensive dimensional data for Square Head Bolts. Includes specifications for Collar (DIN 478) and Short Dog Point (DIN 479) variants.
| Nominal Size (d) | Pitch (P) | Head Width (s) (Across Flats) | Head Height (k) | Collar Ø (d2) (DIN 478 Only) | Dog Point Ø (dp) (DIN 479 Only) |
| M8 | 1.25 | 13 mm | 8 mm | 18 mm | 5.5 mm |
| M10 | 1.50 | 17 mm | 10 mm | 22 mm | 7.0 mm |
| M12 | 1.75 | 19 mm | 12 mm | 25 mm | 8.5 mm |
| M16 | 2.00 | 24 mm | 16 mm | 31 mm | 12.0 mm |
| M20 | 2.50 | 30 mm | 20 mm | 37 mm | 15.0 mm |
| M24 | 3.00 | 36 mm | 22 mm | 45 mm | 18.0 mm |
Engineering Note:
s (Head Width): Tolerance typically h13 or h14. Critical for wrench selection.
d2 (Collar Diameter): Provides the bearing surface area. Essential calculation point for soft material installation (Aluminum/Cast Iron).
dp (Dog Point): Designed to fit ISO 2342 sized holes. Ensure mating hole clearance is roughly +0.2mm to +0.5mm depending on diameter.
Tooling Choice: Do not use 12-point sockets. Use dedicated 4-point or 8-point sockets to maximize contact area and prevent corner damage.
Hole Clearance (ISO 273): Since square heads are often used in recessed channels, ensure the channel corner radius accommodates the diagonal rotation of the square head (Diagonal = 1.414 x Side).
Torque Control: Due to the robust head geometry, Square Head Bolts can withstand higher tightening torque than standard Grade 4.8 hex bolts. However, always calculate torque based on thread friction (K = 0.2 for zinc, K= 0.15 for black oxide).
Related Products
FAQ
What is the difference between a Square Head Bolt and a Carriage Bolt?
A Square Head Bolt (DIN 479) has a four-sided head designed to be turned with a wrench. A Carriage Bolt (DIN 603) has a round head with a square neck underneath, designed to lock into wood and not be turned.
Why use a square head bolt instead of a hex bolt?
Square head bolts are easier to grip with an adjustable wrench in blind spots and are less likely to “cam-out” or strip when the head is rusted or covered in paint. They also offer a rustic aesthetic for period-correct restorations.
What is the purpose of the collar on a DIN 478 bolt?
The collar (or flange) on a DIN 478 square head bolt acts like a built-in washer. It distributes the clamping force over a wider area, preventing the bolt head from sinking into softer materials like aluminum or cast iron.
Can you manufacture ANSI B18.2.1 Square Head Bolts?
Yes, we supply imperial size Square Head Bolts from 1/4″ to 1-1/2″ diameter, adhering to ANSI/ASME B18.2.1 standards for the US market.
What is a "Dog Point" on a square head bolt?
A Dog Point is a cylindrical, unthreaded tip at the end of the bolt. It is used to locate the bolt into a groove or hole on a shaft, preventing rotation or ensuring precise alignment before the threads engage.