Linear shaft size is one of the first details buyers check when designing a linear motion system. Common diameters such as 8mm, 10mm, 12mm, 20mm, 25mm and 30mm linear shafts are widely used in 3D printers, CNC machines, packaging equipment, automation devices and measuring systems. However, shaft diameter should not be selected by size alone.
A larger diameter usually provides better rigidity, but the actual performance of a linear shaft also depends on shaft length, support method, material, surface treatment, bearing matching and installation accuracy. This guide explains how different linear shaft sizes perform in practical applications and how to choose a suitable diameter for your machine structure.
Selection reminder: A linear shaft is usually used together with linear bearings, shaft supports, bearing blocks or supported rail systems. When confirming a model, check the shaft diameter, stroke length, load direction, installation space and matched bearing size together.
Why Linear Shaft Diameter Matters
The diameter of a linear shaft directly affects rigidity, bending resistance and the size of the matched linear bearing. A small shaft is compact and lightweight, but it is easier to bend when the stroke becomes longer or the load increases. A larger shaft gives stronger support, but it also requires more installation space, larger bearings and higher overall system cost.
In real applications, shaft selection is not simply "the bigger, the better." The right choice should balance load, movement smoothness, machine space and budget. For light-duty equipment, 8mm to 12mm shafts may be enough. For medium industrial motion, 20mm is often more stable. For heavier structures or longer support distance, 25mm or 30mm shafts may be considered.
Quick Comparison of Common Linear Shaft Sizes
| Shaft Diameter | General Rigidity Level | Typical Use | Selection Note |
|---|---|---|---|
| 8mm Linear Shaft | Light-duty | Small 3D printers, compact sliders, light positioning mechanisms | Best for short stroke and limited load conditions. |
| 10mm Linear Shaft | Light to general-duty | Desktop machines, small automation units, laser engravers | A practical option when 8mm is too light but space is still limited. |
| 12mm Linear Shaft | Light-medium | Small CNC machines, packaging devices, sorting equipment | A common transition size between compact and medium-duty structures. |
| 20mm Linear Shaft | Medium-duty | CNC feed mechanisms, automation frames, industrial conveyors | Suitable when higher rigidity and better long-term stability are required. |
| 25mm Linear Shaft | Medium-heavy | Heavy packaging machines, larger CNC auxiliary axes, industrial equipment | Better for higher load or longer support distance than 20mm. |
| 30mm Linear Shaft | Heavy-duty support level | Large machine structures, heavy automation, engineering equipment | Use when machine space, support structure and load requirement justify the larger size. |
8mm Linear Shaft: Compact Size for Light Motion
An 8mm linear shaft is usually selected for compact equipment where space is limited and the moving load is light. It is commonly seen in small 3D printers, light optical adjustment structures, small sliders and simple positioning mechanisms.
The advantage of 8mm is compact installation and lower system weight. The limitation is rigidity. If the stroke becomes too long or the bearing span is not arranged well, shaft deflection may affect movement accuracy. For this reason, 8mm shafts should be used mainly in short-stroke, light-load applications.
10mm Linear Shaft: A Practical Light-Duty Option
A 10mm linear shaft provides more rigidity than an 8mm shaft while still keeping the structure compact. It is often used in desktop laser engraving machines, small automation devices, camera sliders, compact measuring systems and light CNC auxiliary mechanisms.
If the machine needs slightly better stability than 8mm but cannot use a larger shaft because of limited space, 10mm is a reasonable choice. It is also easy to match with common linear bearings and shaft support components.
12mm Linear Shaft: Between Compact and Medium-Duty Designs
A 12mm linear shaft is a useful transition size. It is still compact enough for small machines, but its rigidity is better than 8mm and 10mm shafts. This size is suitable for small CNC machines, automation modules, packaging adjustment mechanisms and light industrial equipment.
When a 10mm shaft feels too flexible for the required stroke or load, but a 20mm shaft is too large for the structure, 12mm can provide a better balance between installation space, cost and stability.
Practical tip: For small shafts such as 8mm, 10mm and 12mm, pay close attention to stroke length and bearing spacing. A small shaft may work well in a short mechanism but become unstable when the unsupported length increases.
20mm Linear Shaft: Common Size for Medium Industrial Motion
A 20mm linear shaft is widely used in medium-duty linear motion systems. Compared with smaller shafts, it gives better resistance to bending and is more suitable for continuous industrial use.
Common applications include CNC auxiliary axes, industrial conveyor mechanisms, packaging machinery, printing equipment, woodworking machines and general automation equipment. If the machine needs stable guidance but does not require a square linear guideway system, a 20mm shaft with matched linear bearings can be a practical solution.
25mm Linear Shaft: More Rigidity for Larger Mechanisms
A 25mm linear shaft is suitable for applications where the structure requires more support than a 20mm shaft can provide. It is commonly used in medium-heavy automation equipment, heavy packaging machinery, larger adjustment structures and auxiliary movement systems in industrial machines.
Because 25mm shafts need larger bearings, larger supports and more installation space, the whole system should be checked before selection. If the stroke is long, a supported shaft structure may be more suitable than simply increasing the unsupported shaft diameter.
30mm Linear Shaft: For Heavy Support and Large Structures
A 30mm linear shaft is used when the machine requires higher rigidity, stronger support and better stability under heavier working conditions. It can be considered for large automation equipment, heavy machine structures, engineering machinery and long service mechanisms where smaller shafts may not provide enough stiffness.
The trade-off is clear: a 30mm shaft increases system size, bearing size, support cost and installation weight. Before choosing this diameter, it is important to confirm whether the machine really needs this level of rigidity or whether a supported shaft system is a better structure.
Unsupported Shaft or Supported Linear Shaft?
One common selection mistake is only increasing shaft diameter when the real problem is insufficient support. For short stroke and light load, an unsupported round shaft with end supports may be enough. For longer travel or higher load, a supported linear shaft can reduce deflection because the shaft is supported along its length.
SBR and TBR supported shaft systems are often used when the application needs longer travel, better support and easier assembly with open linear bearing blocks. For example, an SBR20 linear rail may be more stable than an unsupported 20mm shaft in a long-stroke structure.
Match the Linear Shaft with the Correct Linear Bearing
Linear shaft diameter must match the inner diameter of the selected linear bearing. For example, an 8mm shaft should be matched with an 8mm bore linear bearing, while a 20mm shaft should be matched with a 20mm bore bearing or bearing block.
Besides diameter, the shaft surface condition also matters. A properly ground and chrome-plated shaft can help reduce friction, improve wear resistance and support smoother motion. For projects with higher wear requirements, material and surface treatment should be confirmed before ordering.
How to Choose the Right Linear Shaft Size
When choosing a linear shaft size, start from the actual machine structure instead of choosing by diameter alone. The following points should be checked before confirming the model:
- Required shaft diameter and matched linear bearing model
- Total shaft length and effective unsupported span
- Load weight, load direction and movement frequency
- Whether the shaft is end-supported or fully supported
- Material requirement, such as GCr15 bearing steel or C45 high carbon steel
- Surface treatment, hardness, straightness and corrosion protection requirement
- End machining needs such as cutting, drilling, tapping, threading or step machining
For light-duty and compact equipment, 8mm, 10mm or 12mm shafts are often selected. For medium industrial applications, 20mm shafts are commonly used. For larger equipment or higher rigidity requirements, 25mm and 30mm shafts may be more suitable. For long travel applications, supported shaft systems should be considered early in the design.
DLY Linear Shaft Supply and Custom Options
DLY supplies precision linear shafts for automation equipment, CNC machines, packaging machinery, 3D printers, measuring devices and industrial motion systems. Available options include regular linear shafts, chrome plated shafts, soft shafts, supported shaft systems and custom machined shafts according to drawing requirements.
If you are not sure which linear shaft size is suitable, send DLY your shaft diameter, length, quantity, material requirement, matched bearing model or application drawing. Our team can help check the shaft type, support structure and matching components before quotation.
Need linear shaft selection support?
Send your shaft diameter, length, drawing or matched bearing model. DLY can help confirm suitable linear shaft options for your machine structure.
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