What’s the Difference Between R21 and R23 Oil Seals?
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When it comes to shaft sealing, small design details make a big difference. One of the most common questions we’re asked is:
“What’s the difference between an R21 oil seal and an R23 oil seal?”
They look similar, but there’s one key difference, and it affects how and where you use them.
R21 Oil Seals – Single Lip
An R21 oil seal (also known as a TCN or SC type) has a single sealing lip.
That lip maintains contact with the rotating shaft, keeping oil, grease, or fluid inside while preventing leakage. Because there’s only one lip, R21 seals have lower friction and are ideal for clean environments where there’s no significant dust or contamination.
Typical uses:
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Gearboxes and transmissions
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Pumps and hydraulic systems
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Bearings and rotating machinery in clean conditions
In short: R21 = single lip, simple, low friction, for clean environments.
R23 Oil Seals – Double Lip with Dust Protection
An R23 oil seal (sometimes marked TC or SD type) includes two lips:
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The primary lip, which seals the fluid.
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A secondary dust lip, which protects against dirt, dust, and moisture ingress.
That extra lip makes the R23 the better choice for dusty, wet, or outdoor environments — like engines, axles, and industrial machinery.
Typical uses:
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Automotive crankshafts and hubs
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Agricultural or construction machinery
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Outdoor pumps, engines, and hydraulic systems
In short: R23 = double lip with dust lip, added protection for harsh conditions.
Visual Difference
If you look closely:
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R21 has one main sealing lip and a smooth outer edge.
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R23 has an extra, smaller lip on the opposite side — the dust seal — usually visible as a thin ridge.
Material Options
Both types come in a range of materials to suit different fluids and temperatures:
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NBR (Nitrile): General-purpose, oil-resistant, cost-effective.
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FKM (Viton®): High temperature and chemical resistance.
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Silicone: Flexible, clean applications, wide temperature range.
At Selo, we stock R23 NBR oil seals in a wide variety of metric sizes, with more styles and materials coming soon.
Shop R23 Oil Seals → Oil Seals R23/TC – Nitrile Shaft Seals + Garter Spring | SealWithSelo – Seal with Selo
R21 vs R23: Quick Comparison Table
| Feature | R21 (Single Lip) | R23 (Double Lip) |
|---|---|---|
| Number of Lips | 1 | 2 |
| Dust Protection | No | Yes |
| Friction | Lower | Slightly higher |
| Ideal Use | Clean environments | Dusty or outdoor environments |
| Typical Material | NBR, FKM | NBR, FKM |
| Common Applications | Gearboxes, pumps | Engines, axles, industrial use |
In Summary
Both R21 and R23 seals are designed to keep fluids in and contaminants out — but the R23’s dust lip makes it the better all-rounder for most real-world applications.
If you’re replacing a seal and not sure which you need, check for the extra lip on the old one — or feel free to get in touch, and we’ll help identify it.