24x161mm Ss35 Sleeper Screw for Concrete and Timber Sleepers
Oct 23, 2025
The Role of the 24x161mm Ss35 Sleeper Screw
A sleeper screw is a threaded fastener that connects the rail, or the baseplate under the rail, to the sleeper. The 24x161mm Ss35 has a 24 mm nominal shank diameter and a 161 mm length, and it belongs to the Ss series of sleeper screws. It is suitable for both concrete and timber sleepers: on timber it is screwed into a pre-drilled pilot hole, and on concrete it is threaded into a plastic dowel cast into the sleeper. The threaded engagement gives the fastening high pull-out resistance, and because the screw is elastic within its working range, it absorbs longitudinal and lateral loads from train operation instead of passing every impact straight into the sleeper.
Why the Ss35 Is Used on Concrete Sleepers
Concrete sleepers cannot accept fasteners driven directly into the concrete, so the sleeper is manufactured with a plastic dowel cast into the rail seat area. The Ss35 screw is threaded into the dowel, which does three things: it spreads the clamping force over a larger area of concrete, it allows the fastening to be removed and re-used during maintenance, and it insulates the screw from the concrete. This arrangement is the standard way to fasten baseplates and rail assemblies on concrete-sleeper track in many metric-standard markets.
The Ss Series Sizes
The Ss series covers a family of sleeper screws in different diameters and lengths. The table below lists the common sizes with their nominal unit weights.
| Type | Dimension (mm) | Weight (kg) |
|---|---|---|
| Ss5-150 | M24x150 | 0.545 |
| Ss8-140 | M24x140 | 0.528 |
| Ss8-150 | M24x150 | 0.548 |
| Ss8-160 | M24x160 | 0.568 |
| Ss23-160 | M24x160 | 0.645 |
| Ss25-165 | M24x165 | 0.625 |
| Ss35-161 | M24x161 | 0.657 |
Materials, Grades and Mechanical Properties
The strength of a sleeper screw is defined by its material and its property class. The table below shows the common grades and the mechanical values they represent.
| Grade | Typical material | Tensile strength (MPa) | Yield strength (MPa) | Elongation (%) |
|---|---|---|---|---|
| 4.6 | Q235 | 400 min | 240 min | 22 min |
| 5.6 | 35# | 500 min | 300 min | 20 min |
| 8.8 | 45#, 40Cr | 800 min | 640 min | 12 min |
| 10.9 | 40Cr, alloy steel | 1000 min | 900 min | 9 min |
All grades are expected to pass a 90 degree cold bend test without cracking. Grade selection follows the track design: 4.6 and 5.6 cover standard service, while 8.8 and 10.9 are used where the fastening must carry higher clamping force or resist higher dynamic loads. The property classes are referenced to ISO 898-1, and supply can also be referenced to UIC 864-1 and the relevant French national practice for sleeper screws.
Finishes
Sleeper screws are available in a range of finishes: plain with oil film, oxide black, zinc plated, hot-dip galvanized, waxed, bituminous coated, zinc flake, and sherardized. The finish is selected on the same basis as for any outdoor fastener - plain oiled for normal service, zinc or galvanized coatings for coastal and wet environments, and bituminous or zinc flake where chemical resistance is needed. Whatever the finish, it is applied after heat treatment so the mechanical properties of the screw are not affected.
Working with the Complete Fastening
The sleeper screw does not work alone. In a complete fastening the rail sits on a rail pad, the pad on a baseplate, and the screw passes through the plate into the sleeper or dowel. Elastic rail clips may be added to control vertical and lateral rail movement. The screw, pad, plate, and clip must be specified as a set, because their dimensions and stiffness are matched to each other and to the rail section. Specifying the complete assembly from one source avoids mismatches in geometry and keeps the load path straight from the rail into the sleeper.
Frequently Asked Questions
1. What does 24x161mm mean for the Ss35 screw?
It is the nominal shank diameter (24 mm) and overall length (161 mm). The Ss35 defines the collar and thread geometry of this member of the Ss series.
2. Can the Ss35 be used on timber sleepers as well as concrete?
Yes. On timber it is screwed into a pre-drilled pilot hole; on concrete it is threaded into a plastic dowel cast into the sleeper. The dowel makes the fastening demountable and protects the concrete.
3. Which grade should I specify for heavy haul track?
Grade 8.8 or 10.9, with 45# or 40Cr material, is used where the fastening must carry higher clamping force and resist higher dynamic loads. For standard service, grades 4.6 and 5.6 are usually adequate.
4. What standards are referenced for sleeper screws?
Property classes follow ISO 898-1, and supply can be referenced to UIC 864-1 and national practice for sleeper screws. Non-standard profiles are manufactured to the customer's drawing.
5. What finish is best for coastal track?
Hot-dip galvanized, zinc flake, or sherardized finishes give the best corrosion protection for coastal and wet environments. Plain oiled screws should be limited to normal service.
6. How do I install the 24x161mm screw correctly?
Pre-drill the sleeper to the specified pilot hole diameter, or use a sleeper with a cast-in dowel, then drive the screw with a power wrench at controlled torque. Overtightening can strip the dowel thread or crush the timber fibres.
