Steel Shaft and Steel Bar Selection: Grade, Size, Tolerance

Steel shafts and steel bars are fundamental components in machine manufacturing. Gears, pins, fastening bolts, axles, piston rods, or simple bushings—all of these often begin as a round steel bar. However, choosing the wrong steel grade or an unnecessarily tight tolerance can both shorten the service life of the component and increase costs unnecessarily. This guide has been prepared to help you make the right decision when buying steel shafts.

What is the difference between a steel shaft and a steel bar?

In everyday use, the two terms are often used interchangeably. Technically, a steel bar is a general term for long steel products with round, square, hexagonal, or flat cross-sections. A steel shaft generally refers to a solid round bar used for components that rotate or support an axis. Hot-rolled round bars are manufactured according to EN 10060, while cold-drawn bars are manufactured according to EN 10278.

Step 1: Choose the right steel grade for the application

The steel grade should be selected according to the load, wear, impact, and operating conditions the component will be exposed to.

For more information about materials used for high-volume turned parts, see our article What Is Free-Cutting Steel?.

Step 2: Determine the manufacturing method and tolerance

If your component will be turned to its final dimensions, a hot-rolled bar is generally the most economical solution; the next larger diameter is selected to allow sufficient machining allowance. If the component will be assembled without machining its outside diameter, or if you want to reduce machining time, cold-drawn (bright) steel should be preferred. Tolerances for cold-drawn steels are expressed using ISO h tolerance classes:

Uyar Çelik can supply products in tolerance classes ranging from h6 to h12 according to TS EN 10278. Tight tolerances such as h6–h8 are achieved on polished and ground surfaces.

Step 3: Specify the heat treatment condition

Steel shafts of the same grade can have different mechanical properties and prices depending on their heat treatment condition:

• +N (Normalized): Homogeneous structure for general-purpose applications.
• +A (Soft Annealed): Improved machinability for components that will undergo subsequent heat treatment.
• +QT (Quenched and Tempered): High strength ready for use; no additional heat treatment required in the workshop.
• Induction surface hardening: A hard surface layer with a tough core for surfaces exposed to wear.

Steel shaft weight table

The weight per meter of a round steel bar is calculated using the following formula:

• Weight (kg/m) = d² × 0.006165 (d: mm)

For other dimensions, you can use our Uyar Çelik Weight Calculator. The values are theoretical; actual weight may vary slightly depending on manufacturing tolerances.

What affects steel shaft prices?

Steel shaft prices are generally determined on a per-kilogram basis. The main factors affecting the price include:

• Steel grade: The price per kilogram generally increases as alloy content increases.
• Manufacturing method: Whether the material is hot-rolled or cold-drawn.
• Tolerance class: Costs increase as tolerances become tighter.
• Heat treatment condition: +N, +A, +QT, or surface hardening.
• Surface finishing: Additional processes such as peeling and grinding.
• Quantity, cutting, and transportation: Order tonnage and logistics requirements.

When evaluating the total cost, you should consider not only the price per kilogram but also machining time and material waste in your workshop.

Common mistakes when selecting steel shafts

The most common mistakes when ordering steel shafts include:

• Buying material with unnecessarily tight tolerances (h7–h8) for components that will be machined
• Selecting a high-carbon or alloy steel grade for components that need to be welded
• Using a steel grade with insufficient hardenability for large-diameter, heavily loaded shafts
• Ordering hot-rolled bars at the exact finished dimension without allowing for machining allowance
• Failing to request a material certificate for critical components

Surface condition: Cold-drawn, peeled, and ground

Bright steels are classified not only by tolerance but also by their surface condition:

• Cold-drawn: The most common type of bright steel; provides good surface quality and h9–h11 tolerances.
• Peeled (turned): Particularly preferred for larger diameters; surface decarburization and defects are removed by machining.
• Ground and polished: Used for precision shafts requiring tight tolerances such as h6–h8 and low surface roughness.

For components that will undergo heat treatment or induction hardening, it is important that the surface does not contain a decarburized layer. Therefore, choosing a peeled or ground surface for critical shafts makes it easier to achieve the target surface hardness after hardening.

How is machining allowance determined?

For a component that will be turned from hot-rolled bar, the next standard size above the final diameter is generally selected. For example, for a shaft with a finished diameter of Ø45 mm, a Ø50 mm hot-rolled bar is a common choice. Straightness deviation should also be taken into account for long and slender components.

The right shaft at the right price with Uyar Çelik

Uyar Çelik supplies hot-rolled and cold-drawn round bars in a wide range of diameters in accordance with EN and ASTM standards. With custom-length cutting, special-tolerance production, and imported alloy steel bar options, we provide the most suitable solution for your project.

Frequently asked questions

Which steel is used for transmission shafts?

For general applications, C45 (Ck45) is commonly preferred, while 42CrMo4 is used for higher loads. Cold-drawn shafts with h9 tolerance are commonly used for precision bearing applications.

Should I choose a solid shaft or a hollow shaft?

Solid shafts are generally preferred for small- and medium-diameter applications subjected to high torsional and bending loads. For large-diameter applications where weight is critical, seamless steel tubing may be considered.

What is the difference between h9 and h11?

Both are shaft tolerance classes, but h9 has a tighter deviation range. For example, for diameters between 18 and 30 mm, the permitted deviation is 0/-0.052 mm for h9 and 0/-0.130 mm for h11.

Conclusion

Choosing the right steel shaft starts with selecting the appropriate steel grade for the application, the required tolerance, the correct heat treatment condition, and the appropriate surface condition. Choosing an unnecessarily tight tolerance or the wrong steel grade increases costs, while the right selection extends component service life and reduces total production costs. Request a quotation for your steel shaft and steel bar requirements today: +90 (212) 485 98 98 or visit our contact page.