What Is a Rail Screw Spike
A rail screw spike, also known as a sleeper screw, rail screw or lag bolt, is a medium to large metal screw used to fasten a rail base plate or a rail directly to the sleeper. The spike is threaded into a pre-bored hole in a timber or concrete sleeper, often with an embedded plastic dowel that protects the bore and improves pull-out resistance. Screw spikes are a widely specified fastening element in rail fastening systems because they deliver high clamping force, dependable gauge retention and straightforward maintenance.
Main Types of Screw Spikes
Railway screw spikes are classified by head shape and application. The most common families are the sleeper screw series, square head screw spikes, hexagon head screw spikes, and special-purpose products such as Australian AS screw spikes, Tr thread screws and timber screws. Square head spikes are often selected for timber sleepers, while hexagon head spikes with property classes 4.6 to 10.9 suit heavy haul and high speed lines. Each type is engineered with specific thread geometry and hardness to resist pull-out and fatigue under dynamic wheel loads.
Typical Specifications and Materials
The sleeper screw series covers dimensions from M22 x 130 mm to M26 x 150 mm as well as M24 x 140 mm and M24 x 180 mm versions. Unit weights range from about 0.45 kg to 0.70 kg depending on size. Common raw materials include Q235 carbon steel, 35, 45, 55Q and 40Cr alloy steel, with property classes 4.6, 5.6, 8.8 and 10.9 in line with ISO 898-1. As an example, a grade 8.8 hexagon screw spike provides a minimum tensile strength of 800 MPa, a minimum yield strength of 640 MPa and an elongation of 12 percent, and it must pass a 90 degree cold bending test without cracking.
Surface Finishes and Applicable Standards
Surface protection options include plain oiled, oxide black, zinc plating, hot dip galvanizing, Dacromet, sherardizing, wax and bitumen coating. Industry standards referenced for screw spikes include UIC 864-1, AREMA, DIN, GB and AS 1085.18 for Australian screw spikes. Tr thread screws follow NF F 50-015 and UIC 864-1, while high strength spike bolts follow GB/T 3098.1. The standard selection should match the sleeper material, the climatic environment and the line category.
Selection and Installation Considerations
Select the spike diameter and length according to the sleeper type, the base plate hole pattern and the required clamping force. For timber sleepers, pre-drill the bore to the recommended diameter to prevent splitting. For concrete sleepers, install a plastic dowel or threaded insert before driving the screw spike. Apply controlled torque during installation to avoid thread stripping and to achieve a uniform clamping force across the fastening assembly. Verify the spike depth after driving so that the head seats correctly on the base plate.
Safety and Maintenance
Inspect screw spikes at scheduled track maintenance intervals and check for loosening, corrosion and thread damage. Re-torque loose spikes and replace cracked or heavily corroded units immediately. Keep spare spikes and matching plastic dowels in stock so worn components can be replaced quickly. Record torque values and replacement dates to build a reliable maintenance history for the line.
Common Misconceptions
A frequent mistake is assuming that an ordinary bolt can replace a screw spike. Screw spikes are engineered with specific thread geometry, hardness and corrosion protection for dynamic rail service. Another misconception is that zinc plating alone is sufficient for coastal lines; hot dip galvanizing, Dacromet or sherardizing should be specified where humidity and salt exposure are high. A third error is over-tightening spikes, which can strip threads in the dowel and reduce pull-out strength.
Frequently Asked Questions
What is the difference between a screw spike and a dog spike? screw spike is threaded and installed by rotation, giving strong pull-out resistance and easy re-tensioning, while a dog spike is driven by impact, is cheaper to install and is more likely to loosen under heavy traffic.
Which material grades are used for high strength screw spikes? Common materials are Q235 carbon steel, 35, 45 and 55Q steel, and 40Cr alloy steel, with property classes from 4.6 up to 10.9 according to ISO 898-1.
Why is a plastic dowel needed in concrete sleepers? The dowel protects the bore from wear, distributes the clamping force evenly and provides a durable thread for repeated installation and removal of the screw spike.
What surface finishes protect screw spikes from corrosion? Plain oiled, oxide black, zinc plating, hot dip galvanizing, Dacromet, sherardizing, wax and bitumen coatings are available, with hot dip galvanizing preferred for humid and coastal environments.
How often should screw spikes be inspected? Inspection follows the track maintenance schedule of the operator, typically at every routine patrol, with torque checks and visual inspection for corrosion, loosening and thread damage.
Can screw spikes be reused after removal? Reuse depends on thread condition, corrosion level and the results of dimensional checks; damaged threads or heavy corrosion mean the spike should be replaced.
