What Is Bearing Internal Clearance? C3 vs C4 Guide (2026)
Bearing internal clearance is the physical space between rolling elements and raceways, with standard clearance designated as CN for normal industrial operating conditions[1]. This gap is a critical parameter, as operating clearance changes after installation due to interference fits and temperature increases[2]. C3 and C4 clearances provide a larger internal gap than standard CN bearings to accommodate thermal expansion in high-temperature industrial machinery[1].
For plant engineers and mechanics across Indonesia, specifying the correct internal gap prevents costly machine downtime. Heavy industrial applications generate significant heat, causing steel shafts and bearing rings to expand at different rates. If a standard clearance bearing is installed where a C3 or C4 is required, this differential expansion quickly consumes the remaining space, leading to severe friction and rapid component failure. HI-TEC ASIA consults plant engineers to specify the correct C3 or C4 bearing clearance, preventing costly downtime in heavy industrial applications.
What is bearing internal clearance and how does C3 compare to standard?
Bearing internal clearance is the free movement inside an unmounted bearing - the distance one ring can move relative to the other in the radial or axial direction when no external load is applied[3]. In practice, it is a controlled design parameter because the operating clearance changes after mounting, interference fits, and temperature rise[2].
Standard clearance is designated as CN for normal industrial operating conditions[1]. C3 and C4 clearances provide a larger internal gap than standard CN bearings to accommodate thermal expansion in high-temperature industrial machinery[1]. The exact clearance values in micrometers are bearing-size-specific and are defined by the manufacturer's standards tables, rather than by the suffix alone[4].
During operation, the inner ring typically runs hotter than the outer ring. To compensate for differential expansion of the two rings when the inner ring operates at a higher temperature than the outer ring, bearings require incrementally larger gaps[2]. According to standard internal clearance order for radial bearings, the space increases sequentially through C1, C2, CN, C3, C4, and C5[5].
| Clearance Class | Application Criteria | Typical Industrial Use Cases |
|---|---|---|
| CN (Standard) | Normal clearance for standard temperature and fit conditions[1]. | Standard industrial duty, normal temperatures, moderate speeds, and standard fits[1]. |
| C3 (Larger) | Used when moderate thermal expansion or interference fit will reduce clearance in service[1]. | Electric motors, gearboxes, compressors, and high-speed machinery[1]. |
| C4 (Maximum) | Used when thermal reduction of clearance is larger, such as hotter operation or tighter fits[1]. | Demanding environments with higher operating temperatures, heavier loads, or tighter fits than C3 can accommodate[1]. |
Selecting the right fit from our industrial bearing product catalog ensures your machinery operates quietly.
When should you use C4 clearance and what happens if you use the wrong bearing?
You should use C4 clearance when considerable loss of clearance is expected due to severe temperature differences and both rings are interference fit[2]. Installing a standard CN bearing instead of a required C3 or C4 clearance bearing can cause premature failure from thermal expansion exceeding 120 degrees Celsius[6]. HI-TEC ASIA consults plant engineers to specify the correct C3 or C4 bearing clearance, preventing costly downtime in heavy industrial applications.
Above 120 degrees Celsius, standard chrome steel bearings experience structural changes, and dimension stabilizing treatment is necessary to maintain the original bearing size[7]. A standard CN clearance bearing in such conditions substantially increases the risk of clearance loss, preload, overheating and seizure, whereas C3 or C4 are specifically intended to compensate for these effects[6]. Thermal strain has a value which cancels the initial clearance of the radial bearing at elevated temperatures, making operation impossible without the correct gap[8].
Choosing the wrong clearance triggers several destructive failure modes:
- Negative Clearance (Preload): When the gap drops below zero, all rolling elements contact both raceways simultaneously; resistance to rotation increases, sliding replaces rolling, and service life drops toward total failure[9].
- Thermal Run-Away: Increased contact forces raise bearing temperature, causing further clearance loss and creating a thermal run-away condition[10].
- Lubricant Degradation: Higher temperature accelerates grease breakdown, causing loss of film, more friction, and rapid wear[11].
- Catastrophic Seizure: With sustained preload, bearings can seize or suffer spalling, flaking, and raceway pitting, often within a fraction of normal life[12].
To ensure you receive the correct HI-TEC or premium HI-TEC SILVER bearing for your plant equipment, contact our team for expert sizing and supply.
Frequently Asked Questions
What is bearing internal clearance?
Bearing internal clearance is the free movement inside an unmounted bearing - the distance one ring can move relative to the other in the radial or axial direction when no external load is applied[3]. This physical gap is essential to accommodate thermal expansion.
What is the difference between standard and C3 bearing clearance?
Standard clearance is designated as CN for normal industrial operating conditions, while C3 provides a larger internal gap to accommodate thermal expansion[1]. C3 is required when moderate thermal expansion or interference fit will reduce clearance in service[1].
When should I use a C4 clearance bearing?
You should use a C4 clearance bearing in demanding environments with higher operating temperatures, heavier loads, or tighter fits than C3 can accommodate[1]. They are specifically designed for severe conditions where a standard bearing would lose all internal clearance.
What happens if I use the wrong bearing clearance?
Installing a standard CN bearing instead of a required C3 or C4 clearance bearing can cause premature failure from thermal expansion exceeding 120 degrees Celsius[6]. The bearing will lose its internal gap, leading to negative clearance, thermal run-away, and eventual catastrophic seizure[10][9].
References
- Lagerspeling uitgelegd: C3 vs. CN vs. C4 en hoe u de juiste kiest.. https://www.demy-bearings.com/nl/news/bearing-clearance-explained-c3-vs-cn-vs-c4-and-how-to-select/ (2026-01-21)
- Technical Catalogue 2012 | PDF | Bearing (Mechanical). https://www.scribd.com/doc/190043995/Technical-Catalogue-2012 (2025-12-17)
- [PDF] Internal Clearance-Types and Norms. https://www.nsk.com/content/dam/nsk/am/en_us/documents/bearings-americas/TI%20Internal%20Clearance.pdf (2026-07-16)
- Perbedaan Bearing C3 dan C4: Mana yang Tepat untuk Mesin .... https://www.primajayabearing.com/artikel-perbedaan-bearing-c3-c4.html (2026-05-20)
- 7—Fits and Internal Clearance | NSK Global. https://www.nsk.com/tools-resources/abc-bearings/fits-and-internal-clearance/ (2024-07-11)
- Bearing Cross Reference: SKF, NSK, NTN, Koyo, NACHI, FAG & More. https://aimsindustrial.com.au/blogs/product-guides/bearing-cross-reference-guide (2026-05-06)
- Ball Roller Bearings. https://koyo.jtekt.co.jp/en/support/bearing-knowledge/pdf/catb2001-8_a.pdf (2026-07-11)
- Effects of operation temperature on thermal expansion and .... https://scispace.com/pdf/effects-of-operation-temperature-on-thermal-expansion-and-6gphpfqnnx.pdf (2026-06-23)
- Bearing clearance, operating clearance and preload - Bearing Wizard. https://bearingwizard.com/bearing-selection-calculation-principles/bearing-clearance/ (2022-03-09)
- Managing Thermal Expansion in High-Performance .... https://thebearingspecialists.co.uk/when-heat-strikes-managing-thermal-expansion-in-high-performance-bearing-applications/ (2026-01-06)
- ®. https://www.fyh.co.jp/fyh.co.jp/wp-content/uploads/2022/09/catno3320_FYH_e.pdf (2024-02-28)
- [PDF] SKF high temperature bearings. https://cdn.skfmediahub.skf.com/api/public/0901d19680998b29/pdf_preview_medium/0901d19680998b29_pdf_preview_medium.pdf (2026-07-14)