How to Specify Oil Seals: A Buyer's Checklist
A complete buyer's checklist for specifying rotary shaft oil seals — covering shaft diameter, bore, width, lip type, material, spring, dust lip configuration, and the 12 data points every quote request should include.
Why oil seal specification fails so often
Oil seals (also called rotary shaft seals or radial lip seals) are the most under-specified component in rotating equipment. A typical maintenance request reads "I need an oil seal for our gearbox" — which is missing every piece of information needed to actually source the part. The result: wrong part shipped, downtime extended, and re-orders that cost 3× the original part value.
This checklist gives you the exact data points to capture before requesting a quote, so the right seal arrives on the first try.
The 12-point oil seal specification checklist
1. Shaft diameter (d1)
The outside diameter of the rotating shaft, in millimeters or inches. Measure with a micrometer at three locations 120° apart and report all three values — shaft wear or out-of-roundness directly affects seal selection.
2. Bore (housing) diameter (d2)
The inside diameter of the housing into which the seal is pressed. This is typically a slip-fit nominal dimension; check the manufacturer's housing tolerance class.
3. Seal width / axial thickness (b)
The total width of the seal across the housing bore. Standard widths are 7, 8, 10, and 12 mm for industrial seals; aerospace and automotive use other standards.
4. Shaft surface speed
Calculated as π × shaft_diameter × RPM. Express in meters per second or feet per minute. Surface speed determines maximum sealing capability and required compound:
- < 4 m/s: any standard NBR or FKM
- 4–8 m/s: high-quality NBR or FKM with smooth shaft finish
- 8–15 m/s: PTFE-faced or specially designed seals
- > 15 m/s: requires custom engineering
5. Operating temperature range
Both continuous and peak temperatures, in °C or °F. The seal compound must handle both ends of the range.
6. Sealed media
The fluid the seal is retaining: mineral oil grade, synthetic gear oil, hydraulic fluid type, water, grease, etc. Include the fluid manufacturer and product name when possible.
7. Pressure rating
Standard radial lip seals are designed for atmospheric or near-atmospheric pressure (< 0.5 bar). Higher pressures require pressure-rated lip designs (PTFE-energized, specially profiled lips).
8. Lip type / profile
| Type Code | Configuration | Use Case |
|---|---|---|
| SC / TC | Single lip with metal case + rubber-covered OD | General industrial, oil retention |
| TB | Single lip with rubber OD only | Soft housing materials, vibration absorption |
| SB | Single lip with metal OD | Standard rigid housings |
| TC4 / TCV | Double lip with dust lip | Dirty environments (gearboxes, off-highway) |
| VRing | All-rubber axial lip seal | Slow-speed protection, low-cost dust exclusion |
| HMS5 / HMSA10 | SKF-style designations for rubber-OD seals | Industry-standard retrofit |
9. Spring (garter spring) presence
Most oil seals include a stainless-steel garter spring that maintains lip-to-shaft contact pressure. Confirm whether the application needs spring (yes for liquids, often no for grease retention).
10. Direction of rotation
For unidirectional helical-pumping seals (ERIKS R-style), specify clockwise or counterclockwise as viewed from the seal face.
11. Shaft surface finish
Critical and often forgotten. Optimal range: 0.2–0.8 µm Ra, plunge-ground (no helical lay). A shaft polished too smoothly (< 0.1 µm Ra) actually causes seal failure due to lack of lubrication retention.
12. Shaft hardness
Minimum 30 HRC for standard service, 45+ HRC for abrasive media. Soft shafts wear quickly under the seal lip, opening leak paths.
Standard oil seal designation example
A typical ERIKS oil seal specification:
TC 25 × 47 × 7 NBR
- TC — standard single-lip seal with metal case, rubber-covered OD
- 25 — shaft diameter (mm)
- 47 — bore diameter (mm)
- 7 — width (mm)
- NBR — nitrile rubber compound
This is the absolute minimum — a complete RFQ should include all 12 checklist points above.
Material selection quick guide
| Compound | Temperature | Best For |
|---|---|---|
| NBR | −40 °C to +100 °C | Standard mineral-oil-based industrial gearboxes, hydraulic motors |
| HNBR | −30 °C to +150 °C | High-temp gearboxes, automotive transmissions |
| FKM (Viton) | −20 °C to +200 °C | Synthetic oils, high-temp engines, aggressive media |
| Silicone (VMQ) | −60 °C to +180 °C | Wide-temperature applications, dry running |
| PTFE | −100 °C to +260 °C | High-speed shafts, dry/lubricant-starved conditions, chemical attack |
The five most common oil seal failure modes
- Hardening and cracking — temperature exceeded compound rating; upgrade material
- Lip wear / groove formation on shaft — shaft surface too rough or hardness too low
- Spring loss / dislodgement — installation damage or excessive pressure
- External contamination — single-lip seal used in dirty environment; should be double-lip TC4
- Reverse-pressure failure — seal installed backward or pressurized from wrong side; use bidirectional design
Frequently Asked Questions
Can I substitute one oil seal compound for another with the same dimensions?
Only if the substitute compound covers the operating temperature, fluid compatibility, and surface speed of the original. Always verify the technical datasheet — dimensional interchangeability does not equal functional interchangeability.
What's the difference between an oil seal and a V-ring?
Oil seals (radial lip seals) are pressed into a housing and seal radially against the shaft. V-rings are stretched onto the shaft and seal axially against a counterface — typically used for dust exclusion in dirty environments.
How do I measure an oil seal that has no markings?
Use a digital caliper to measure the shaft (ID), the housing bore (OD), and the seal width. Note the lip configuration (single, double, with/without dust lip) and the spring presence. With those five data points, ERIKS or your distributor can match the seal in 95% of cases.
What surface finish does my shaft need under an oil seal?
0.2–0.8 µm Ra, plunge-ground (no helical lay from turning). Avoid shafts that are too smooth (< 0.1 µm Ra) because they lack the micro-asperities that retain a hydrodynamic film under the seal lip.
Where can I buy ERIKS oil seals in the United States?
Tereefek Solutions stocks the full ERIKS oil seal range — single-lip, double-lip, PTFE-faced, and custom configurations — in NBR, HNBR, FKM, silicone, and PTFE. Browse the oil seal catalog by shaft × bore × width, or request a quote with the 12-point checklist above.
One-page printable RFQ template
Copy and paste this template into your next quote request to get same-day pricing with no follow-up questions:
Application: __________________________ Shaft diameter (d1): _______ mm Bore diameter (d2): _______ mm Width (b): _______ mm Sealed media: _______________ Operating temperature (continuous / peak): _____ / _____ °C Shaft RPM (max): _______ Lip type (TC / TC4 / TB / other): _______ Compound preference (NBR / HNBR / FKM / silicone / PTFE): _______ Direction of rotation: _______ Shaft surface finish (µm Ra): _______ Quantity required: _______