The integrity of a railway track depends heavily on the humble hardware holding it together, and precise railroad spike dimensions are critical for ensuring that rails remain securely fastened to ties under the immense pressure of passing trains. A spike that is too short may pull out under vibration, while one with the wrong shank width could split the wooden tie, compromising the track gauge. Understanding the specific measurements, weight classes, and material standards is essential for track engineers, maintenance crews, and industrial contractors.
Railroad Spike Dimensions
When discussing railroad spike dimensions, we refer to specific standardized measurements that determine a spike’s holding power. The primary measurement is the length, but unlike standard nails, railroad spikes are measured from the underside of the head to the tip of the point. This “length under head” ensures that the fastener penetrates the tie to the required depth regardless of the head’s thickness.
The second critical dimension is the shank cross-section. Most traditional “dog” or “cut” spikes feature a square shank. This square geometry provides approximately 50% more holding power than a round shank of equal metal volume because it cuts through the wood fibers, creating a friction bond that resists pull-out forces. Standard industrial spikes typically follow ASTM A65 or AREMA (American Railway Engineering and Maintenance-of-Way Association) specifications, which strictly dictate tolerances for length, straightness, and head angle.
Standard Railroad Spike Dimensions and Classes
To accommodate different rail weights and traffic loads, spikes are categorized by size and material grade. The two primary material designations are Low Carbon (Soft Steel) and High Carbon.
Class 1 (Soft Steel) Dimensions
Class 1 spikes are typically used in industrial sidings, light rail, or mining operations where flexibility is more critical than maximum tensile strength. They generally follow the same dimensional standards as high-carbon spikes but are often found in smaller sizes.
- Common Applications: Turnouts, lighter rail sections (under 85 lbs/yd), and temporary tracks.
- Dimensional Tolerance: The shank width generally has a tolerance of ±1/32 inch, while the length can vary by ±1/8 inch.
Class 2 (High Carbon) Dimensions
For mainline freight and high-speed passenger lines, Class 2 spikes are the standard. The high carbon content (marked “HC” on the head) provides greater resistance to bending and shearing.
- Common Size: The 5/8″ x 6″ spike is the industry workhorse for standard gauge track using 90 lb to 136 lb rail.
- Head Design: The head is specifically angled (usually 13 degrees) on the underside to match the slope of the rail base, ensuring maximum contact area.
Common Sizes Breakdown
- 5/8″ x 6″: The definitive standard for heavy rail. It has a 5/8-inch square shank and a 6-inch length under the head.
- 9/16″ x 5 1/2″: Frequently used for older tracks, lighter rail sections (60-85 lbs), or secondary lines.
- 1/2″ and Smaller: Spikes with 1/2″ or 3/8″ shanks are often reserved for mining tracks (narrow gauge) or specialized industrial applications.
Types of Railroad Spikes and Their Design
While the “cut spike” is the most recognizable, variations in design lead to differences in railroad spike dimensions.
Dog Spikes (Cut Spikes)
The traditional cut spike is named for its head, which looks vaguely like a dog’s head with floppy ears.
- Point Dimensions: The point is chisel-shaped (wedge point) rather than conical. This wedge is driven across the grain of the wood. A standard 5/8″ spike typically has a point length of 1 1/4 to 1 1/2 inches.
- Head Offset: The head is offset to hook over the rail flange. The dimensions of this overlap are critical; if too short, it won’t grip the rail; if too long, it risks hitting the web of the rail during installation.
Screw Spikes
Screw spikes offer superior holding power and are increasingly common in modern tracks, especially on curves or turnouts.
- Diameter: Unlike the square shank of a cut spike, screw spikes have a round shank with threads. Common diameters are 22mm or 24mm (approx. 7/8″ to 1″).
- Length: They typically range from 6 to 7 inches to ensure deep engagement with the tie.
- Head: The head usually features a rectangular or square drive top, sometimes with a washer integrated or separate, altering the vertical dimension requirements.
Lock Spikes
These are specialized spikes designed to fill the hole of a worn spike or lock a tie plate in place. They often feature hair-pin-style split shanks that spring open once driven into the tie, creating dimensionally wider holding profiles inside the wood than at the entry point.
Material Specifications and Manufacturing Standards
The manufacturing process directly influences the consistency of railroad spike dimensions. Spikes are generally hot-forged. Steel bars are heated to over 2000°F and then fed into spike machines that cut the shank to length, form the point, and upset the head in a single continuous operation.
Chemical Composition:
- Carbon: Soft steel contains 0.06% to 0.12% carbon, while High Carbon spikes contain 0.20% to 0.30% carbon.
- Copper: Sometimes added (0.20% min) for corrosion resistance in “Copper-Bearing” spikes.
Mechanical Properties:
- Tensile Strength: High carbon spikes must withstand tensile forces of over 70,000 psi.
- Bend Test: A critical dimensional test involves bending the spike cold through 120 degrees. The spike must not crack on the outside of the bent portion, ensuring the metal has sufficient ductility despite its hardness.
Railroad Spikes Specification Table
The following table outlines the standard sizes available in the market. Note that weight per keg is standard across the industry (usually 200 lbs or 50 kg), so the quantity per keg changes based on the individual spike weight.
|
Spike Size (Shank x Length) |
Length Under Head (in) |
Shank Width (in) |
Head Width (in) |
Head Length (in) |
Approx. Weight (lbs/spike) |
Quantity per 200 lb Keg |
|
5/8 x 6 |
6.0 |
0.625 |
1 1/4 |
1 1/2 |
0.82 – 0.86 |
230 – 240 |
|
5/8 x 5 1/2 |
5.5 |
0.625 |
1 1/4 |
1 1/2 |
0.76 – 0.78 |
255 – 260 |
|
9/16 x 5 1/2 |
5.5 |
0.5625 |
1 1/8 |
1 3/8 |
0.64 – 0.68 |
290 – 310 |
|
9/16 x 5 |
5.0 |
0.5625 |
1 1/8 |
1 3/8 |
0.58 – 0.62 |
320 – 340 |
|
1/2 x 4 1/2 |
4.5 |
0.500 |
1 |
1 1/4 |
0.42 – 0.45 |
440 – 475 |
|
1/2 x 4 |
4.0 |
0.500 |
1 |
1 1/4 |
0.38 – 0.40 |
500 – 525 |
|
3/8 x 3 1/2 |
3.5 |
0.375 |
3/4 |
1 |
0.20 – 0.22 |
900 – 1000 |
|
3/8 x 3 |
3.0 |
0.375 |
3/4 |
1 |
0.17 – 0.19 |
1050 – 1150 |
Head Design Dimensions
The dimensions of the spike head are as critical as the shank. The underside of the head is sloped to match the rail base. Standard rail bases (like 115 RE or 136 RE) typically have a 1:40 cant or specific slope angles. The spike head angle is manufactured to ensure that when the spike is driven fully, the entire underside of the head makes contact with the rail base.
If the head dimensions are incorrect:
- Point Loading: The spike contacts the rail only at the edge or the heel. This creates stress concentrations that can snap the spike head off under the cyclic loading of passing trains.
- Throat Cutting: If the neck (the portion of the shank just below the head) is not properly dimensioned or reinforced, the sharp edge of the rail base can cut into the spike over time, thinning it and reducing its strength. This is why many heavy-duty spikes feature a “reinforced throat” dimensionally thicker near the head.
Installation Tolerances
Even with perfect manufacturing, railroad spike dimensions must be respected during installation.
- Vertical Alignment: Spikes must be driven vertically. A spike driven at an angle changes the effective dimensions of the hold and can damage the tie.
- Depth: Spikes should not be over-driven. Over-driving crushes the wood fibers under the head and can cause the head to snap. There should be a nominal gap (often 1/8 inch) or just-touch contact to allow for the rail wave motion without pulling the spike out.
- Pattern: The pattern in which spikes are driven (e.g., 4 spikes per plate vs. 6 spikes per plate) effectively changes the dimensional footprint of the fastening system, distributing the lateral loads across a wider area of the tie.
Railroad Spike Dimensions FAQs
What is the standard size of a railroad spike?
For standard gauge commercial and freight railroads in North America, the standard spike size is 5/8 inch square shank by 6 inches long (measured under the head). This size offers the optimal balance of holding power and durability for 90-140 lb rail sections.
How are railroad spikes measured?
Railroad spikes are not measured by their total overall length. They are measured from the underside of the head (where it meets the shank) to the very tip of the point. The shank width is measured across the flat square section, not diagonally.
What is the difference between Class 1 and Class 2 spikes?
Class 1 spikes are made of soft, low-carbon steel and are generally used for lighter industrial or mining tracks. Class 2 spikes are made of high-carbon steel, offering higher tensile strength and resistance to bending, making them mandatory for mainline freight and passenger tracks.
Why do railroad spikes have a square shank?
The square shank provides superior holding power compared to a round nail. When driven, the square edges cut through the wood fibers and compress them against the flat sides of the shank, creating high friction and resisting the tendency of the spike to rotate or loosen under vibration.
Do screw spikes have different dimensions?
Yes. Screw spikes are cylindrical with a threaded shank, differing significantly from the smooth square shank of cut spikes. They are typically wider (around 7/8″ to 1″ diameter) and require pre-drilled holes in the ties that match the root diameter of the threads for proper installation.
Whether sourcing spikes for a landscaping project, a mining operation, or a Class I railroad, adherence to railroad spike dimensions is non-negotiable. The specifications set forth by organizations like ASTM and AREMA ensure that every spike, from the smallest 3/8″ mining spike to the robust 5/8″ HC mainline spike, performs predictably. By matching the correct shank size, length, and material grade to the rail section and expected load, engineers ensure the safety and longevity of the track infrastructure.
