Dog Spike and Screw Spike Basics
The dog spike is a forged spike with an offset head whose underside matches the rail base profile. It is driven into the sleeper with a spike hammer, and the head clamps the rail foot against the sleeper or tie plate. Its name comes from the two lugs on either side of the head, which resemble a dog's head. The screw spike (also called a rail screw or sleeper screw) has a threaded shank and a square or hexagon head; it is rotated into a pre-drilled hole and pulls the rail down with the thread, which gives a much higher pull-out resistance than a driven spike of the same shank size.
Comparison: Dog Spike versus Screw Spike
| Feature | Dog spike | Screw spike |
|---|---|---|
| Best suited for | Wooden sleepers | Concrete sleepers (with dowel) and timber |
| Installation | Hammered in with a spike hammer | Screwed into a pre-drilled hole with a wrench or machine |
| Holding power | Lower | Significantly higher, typically several times the pull-out resistance |
| Maintenance | Harder to remove and re-tighten | Easier to remove and re-tighten, better maintenance efficiency |
| Cost | Lower | Higher |
Why They Are Not Interchangeable
A dog spike cannot replace a screw spike in concrete because it has no thread to grip the dowel or anchoring material; it would only wedge in the hole and loosen under traffic. Conversely, a screw spike can technically be driven into timber, but the thread cuts the wood fibres and reduces the pull-out resistance below that of a properly driven dog spike, while increasing installation effort. The correct answer to the replacement question is therefore: select the spike by sleeper type. On a wooden-sleeper line, dog spikes are the economical standard; on concrete sleepers, screw spikes with plastic dowels or anchoring are required. Where a line is being upgraded from timber to concrete sleepers, all the spikes must be replaced as part of the sleeper renewal, not one by one.
Pull-Out Resistance and Load Behaviour
Pull-out resistance is the key performance number. A screw spike anchored in a concrete sleever dowel resists vertical uplift several times better than a dog spike in timber of the same shank size, which is why screw spikes are used on heavy-haul and high-speed lines where uplift forces are large. However, the screw spike is less tolerant of lateral thrust in some installations: the thread concentrates the load, so on sharp curves with strong lateral forces the fastening design must add gauge plates or shoulders to share the lateral load. This is also why screw spikes are the standard choice in turnout areas, where the combination of vertical and lateral loads is highest.
Sleeper Screw Specifications
| Type | Specification | Weight (kg) | Surface | Standard |
|---|---|---|---|---|
| Ss 1/130 | M22x130 | 0.451 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
| Ss 1/150 | M22x150 | 0.478 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
| Ss 2/180 | M22x180 | 0.595 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
| Ss 5/150 | M24x150 | 0.545 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
| Ss 6/150 | M26x150 | 0.702 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
| Ss 8/150 | M24x150 | 0.548 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
| Ss 23/160 | M23x160 | 0.645 | Zinc, plain, black oil | UIC, AREMA, JIS, GB |
Common dog spikes are made of low-carbon steel (A3 or Q235 class) with a square shank of 16 mm per side and lengths around 165 mm, manufactured to the current GB/T 702 dimensional standard. Materials for screw spikes range from Q235 (grade 4.6) through 35# (grade 5.6) to 45# (grade 8.8), with zinc, plain or black-oil finishes according to the order.
Selection Guidance
Sleeper material decides the spike family: timber to dog spike, concrete to screw spike.
For mixed turnouts, match each rail seat to its sleeper type and document the pattern for maintenance.
Check the rail base and tie plate hole pattern before ordering the spike size.
Specify the surface treatment by environment: zinc for standard, hot-dip galvanizing for coastal, insulating material for electrified sections.
Order samples and trial-drive them before mass production, especially for timber with unusual hardness.
Frequently Asked Questions
Q: When was the dog spike invented?
A: The dog spike appeared in the early 1830s, and the screw spike followed around 1860. The screw spike spread quickly on main lines because its thread holds much better under heavy traffic.
Q: Which spike is cheaper over the whole service life?
A: The dog spike is cheaper to buy and install, but the screw spike is cheaper to maintain because it can be removed and re-tightened with a wrench, which reduces labour during track renewal.
Q: Can a screw spike be hammered like a dog spike?
A: No. The thread must be rotated into the hole; hammering damages the thread and the dowel. Use a torque wrench or an automated screwing machine, and control the final torque to the drawing value.
Q: Why are screw spikes used in turnouts?
A: Turnout areas carry the highest combination of vertical, lateral and longitudinal loads, and the rails must be re-aligned frequently. The screw spike's high pull-out resistance and easy re-tightening suit this repeated maintenance.
Q: What size of screw spike is common for 60 kg/m rail?
A: M24x150 mm or M24x160 mm screw spikes with grade 8.8 steel are common for 60 kg/m rail on concrete sleepers, matched with a PA66 dowel and the correct torque from the system drawing.