Two Fasteners, Two Mechanisms
A rail spike and a rail clip both hold a rail to a sleeper, but they do it in different ways. A cut spike or screw spike is a driven or turned fastener that bears on the rail foot through the base of the head and transfers load to the sleeper through shank friction and bearing against the timber. A clip is a pre-formed elastic steel bar that is installed in a shoulder or housing and deflects to press the rail foot down with a defined clamping force; the load path is through the clip toe, the rail foot, the rail pad and the sleeper shoulder. The first is a friction and bearing restraint, the second is a controlled elastic restraint with a known toe load, typically in the range of 9 kN to 12 kN for heavy duty elastic clips.
Where a Clip Can Replace a Spike
A clip can replace a spike wherever the sleeper and the fastening assembly provide a proper anchor for it. In practice this means concrete sleepers with cast-in or glued-in shoulders, or timber sleepers fitted with screw-in shoulders or screw spikes that accept a clip, and a rail pad of the correct stiffness between rail and sleeper. This configuration is the standard arrangement on ballasted track with concrete sleepers, and it is qualified as a system against the requirements of the EN 13481 series, with longitudinal restraint measured by EN 13146-1 and torsional resistance by EN 13146-2. Where a track is already built to that system, replacing spikes with clips is a fastening upgrade rather than an experimental change.
Where Spikes Still Have a Job
Spikes retain specific roles. On timber sleeper track, the cut spike remains the conventional and economical fastener, and its withdrawal resistance depends directly on the timber, the spike hole condition and the moisture history of the sleeper. Spikes are also widely used for temporary works, for holding gauge on a timber sleeper during a possession, and in the secondary restraint role on some plate and shoulder assemblies. A clip cannot be installed into a plain timber sleeper without a shoulder or a screw anchor, so in that structure the question is not clip versus spike in the abstract but whether the sleeper can accept a clip at all.
| Comparison point | Rail spike | Elastic rail clip |
|---|---|---|
| Load mechanism | friction and bearing in the sleeper | deflected elastic toe force |
| Clamping force | not defined, depends on driving | defined, typically 9 kN to 12 kN |
| Longitudinal restraint | limited and variable | verified to EN 13146-1 |
| Typical sleeper | timber | concrete, or timber with shoulders |
| Removal and reuse | damages the hole each cycle | clip is reusable, housing is permanent |
| Installation | manual or mechanised driving | manual or mechanised insertion |
Technical Consequences of the Change
Converting a track from spikes to clips is not only a substitution of parts; it alters the mechanical behaviour of the track. A clip applies a sustained vertical clamping force, which increases the torsional resistance of the rail and reduces rail roll, and it provides repeatable longitudinal restraint, which helps the distribution of thermal force in continuously welded rail. The same clamping force also loads the rail pad continuously, so the pad becomes a functional component that must be selected for the required stiffness and for the temperature range of the site. Insulation matters on track with track circuits: the fastening assembly must maintain the required electrical resistance, which is a system design issue rather than a clipping issue.
One caution is common to the conversion of any track: the sleeper must be capable of accepting the fastener. Spiking an existing hole repeatedly enlarges it, and a timber sleeper whose spike holes are enlarged or rotten will not hold a new fastener of any kind. Condition assessment of the sleeper, and not only of the fastener, is therefore part of the decision.
Conversion Checklist
A conversion should be planned as a defined scope of works with the following checks completed before the first fastener is changed: confirm the sleeper type and its condition; confirm the fastening assembly is qualified for the track category, axle load and curve radius under the EN 13481 series; confirm the required rail pad stiffness and the pad thickness that keeps the clamping force correct; confirm the seat and the rail foot are clean and undamaged, since rust and debris change the effective toe load; confirm the clip installation and removal tools are available for the possession; and record the fastening type and the rail temperature during the work so that the change is traceable.
Frequently Asked Questions
Q: Can rail clips be used on timber sleepers?
A: Yes, where the sleeper is fitted with screw-in shoulders or screw spikes of the correct type, or where a plate and shoulder assembly is used. A plain timber sleeper with no anchor cannot take a clip, and the clip will not hold gauge reliably.
Q: Does a clip provide more holding force than a spike?
A: Compared with a cut spike, yes in a practical sense: an elastic clip delivers a defined clamping force, typically around 9 kN to 12 kN, with verified longitudinal and torsional restraint under the EN 13481 series. A cut spike relies on friction and bearing in the timber, and its restraint degrades as the spike hole wears.
Q: Is one type more tolerant of gauge widening in curves?
A: An elastic clip with properly qualified lateral restraint is generally more consistent in curves than spikes, because the restraint is repeatable fastener to fastener. However, curve performance depends on the whole system, including pad stiffness, sleeper condition and the shoulder, not on the clip alone.
Q: Are clips reusable after removal?
A: The clip itself is normally reusable if it is not deformed, cracked or excessively corroded, and it should be inspected for section loss at the toe and at the bend before reuse. The shoulder or housing that anchors it is a permanent sleeper component and is not normally replaced during routine fastener work.
Q: Does the change affect track circuits?
A: It can. The fastening assembly must preserve the required electrical resistance in track circuited areas, which means the pad and any insulating components are specified for that duty. This is a design requirement to be confirmed before conversion, not an afterthought.
