The Job a Spike Has to Do
A spike holds the rail foot (or the baseplate) down against the sleeper and resists the vertical, lateral and longitudinal forces that a passing wheel generates. The rail tries to lift at the foot, push sideways on curves, and creep along the line; the spike must hold all three. Dog spikes and screw spikes do the same job with different mechanics: a dog spike is an interference fit driven into the wood, while a screw spike is a threaded fastener whose withdrawal resistance comes from the thread engaging the timber along its full length.
Design and Installation Differences
| Aspect | Dog spike | Screw spike |
|---|---|---|
| Geometry | Pointed shank, flat head resembling a dog's head in older patterns | Helical thread along the shank, square or round head for wrenching |
| Installation | Driven with a spike maul or mechanical driver | Twisted into a pre-drilled pilot hole with a wrench or rail drill machine |
| Withdrawal resistance | Moderate; depends on timber density and condition | Typically 2-3x a driven spike in sound timber |
| Reuse and re-tightening | Not practical; once loose it must be re-driven or replaced | Can be unscrewed, replaced or adjusted; re-tightenable |
| First cost | Lower per piece | Higher per piece |
| Sleeper types | Timber only | Timber and concrete (with cast-in insert or resin anchor) |
Withdrawal Resistance and Gauge Retention
Withdrawal resistance is the number that decides long-term gauge. A screw spike engages the timber along a threaded length often two to three times the depth of penetration of a comparable dog spike, so in sound timber it holds roughly two to three times the pull-out force. That advantage shows up on curves and at rail joints, where lateral forces are highest: screw-spiked track keeps gauge noticeably better and needs fewer re-spiking operations. The cost is sensitivity to the pilot hole: an undersized hole splits the sleeper, an oversized hole or a worn drill bit leaves the thread with nothing to bite, and the spike spins. Field rules are to drill to the spike manufacturer's diameter, keep the drill perpendicular, and replace the bit on schedule.
Installation Speed and Equipment
Dog spikes win on raw installation speed: a mechanical driver or even a skilled crew with mauls can drive them in seconds, and no drilling is needed. Screw spikes require a drilling pass and then a screwing pass, so first installation is slower, but the screw pass itself is fast with a hydraulic or battery spike driver. The real time saving of screw spikes appears in maintenance: a loose screw spike is re-tightened in place, while a loose dog spike must be withdrawn and re-driven, and re-driving in the same hole almost never restores full holding power because the wood fibres are already damaged.
Maintenance, Reuse and Cost Over Life
Unit price favours the dog spike, and on low-value temporary track that may settle the decision. On mainline, curve-heavy or jointed track, the screw spike's re-tightening ability and higher holding power usually pay back the initial premium over the life of the sleepers. When sleepers are reused, screw spikes are extracted without damaging the timber, and new spikes can be set in the same holes if the wood is sound; dog spike extraction tears the wood around the hole. Corrosion protection matters for both: spikes are supplied galvanized or otherwise protected where moisture is present, because a corroded shank loses section and holding power at the same time.
Selection Guidance by Application
Timber sleeper mainlines and curves: screw spikes, pre-drilled, for holding power and gauge retention; re-tighten at maintenance cycles.
Temporary and industrial lines: dog spikes for speed and low first cost; inspect for loose spikes at each patrol.
Concrete sleepers: screw spikes into cast-in inserts or resin-anchored dowels; dog spikes have no application.
Wet or decayed timber: neither spike holds well; renew the sleeper rather than re-spike, and if screw spikes are used verify the pilot hole in the sound wood only.
High lateral force locations (joints, tight curves, switch areas): screw spikes, with pull-out testing to the project requirement.
FAQ
Which spike holds better, dog or screw?
A screw spike, typically two to three times the withdrawal resistance of a comparable dog spike in sound timber, which is why it holds gauge better on curves and at joints.
Can dog spikes be used on concrete sleepers?
No. Concrete sleepers require screw spikes into cast-in inserts or resin-anchored dowels; a dog spike has no way to engage concrete.
Why do screw spikes need a pilot hole?
The threaded shank needs wood to bite into; without a pilot hole the spike either splits the sleeper or the thread fails to engage evenly. Drill to the manufacturer's diameter, perpendicular to the sleeper surface.
Are dog spikes cheaper in the long run?
Only on temporary track. On mainline track the higher unit cost of screw spikes is usually repaid by fewer re-spiking operations and better gauge retention over the sleeper life.
How is a loose dog spike repaired?
It must be withdrawn and re-driven or replaced; re-driving into the same damaged hole rarely restores holding power. A loose screw spike is simply re-tightened.
What testing is used to verify spike holding power?
Pull-out testing to the project specification, usually a percentage of nominal withdrawal load, performed on sample sleepers after installation and after maintenance cycles.