An oil seal that is the right size but wrong type will fail. One that is right type but wrong material will last months instead of years. Oil seal selection involves three decisions: type (TC/SC/VC/TCV), material (NBR/FKM/PTFE), and size (bore Ã, OD Ã, width). This guide walks through each decision systematically.
Decision 1, Seal Type
TC, Double Lip Seal
The most common oil seal type. Has two sealing lips, a primary (main) lip that runs against the shaft, and a secondary dust lip that faces outward to keep contamination away from the primary lip. The metal case is fully covered in rubber for a good housing bore fit.
Choose TC when: Standard oil or grease sealing against both oil leakage and external contamination. The go-to choice for gearboxes, pumps, motors and most general industrial equipment. 70% of oil seal applications use TC type.
SC, Single Lip Seal
Single primary sealing lip only. No dust protection lip. The metal case is exposed on the outer face. Simpler construction, slightly lower friction than TC.
Choose SC when: The application has its own external sealing provision (a separate labyrinth or external shield), or where the back-side of the seal is exposed to the medium being sealed (lubricant on both sides). Also for higher shaft speeds where the reduced lip friction of a single lip matters.
VC, Open Metal Case, Single Lip
Similar to SC but the outer diameter is a bare metal case rather than rubber-covered. The metal case requires a close fit to the housing bore and a press-in installation.
Choose VC when: Housing bore material is not suitable for rubber OD (very hard materials, or cases where rubber OD might rotate with the housing rather than seal). VC requires more precise housing bore tolerance.
TCV, Double Lip with Metal Insert Exposed
Double lip (like TC) but with an exposed metal OD. Combines the contamination protection of dual lips with the rigid metal case.
Choose TCV when: High contamination environment with heavy external splash (water, slurry) that needs the dual-lip protection, but the application also needs the dimensional stability and press-fit certainty of a metal OD.
Decision 2, Seal Material
| Material | Temp Range | Chemical Resistance | Best For |
|---|---|---|---|
| NBR (Nitrile) | −40°C to +120°C | Mineral oil, hydraulic fluid, water | General industrial, gearboxes, pumps, most machinery |
| FKM (Viton) | −20°C to +200°C | Synthetic oils, fuels, acids, solvents | High-temp applications, chemical process equipment, automotive |
| PTFE | −60°C to +200°C | Virtually all chemicals, acids, bases | Food processing, pharmaceutical, aggressive chemical media |
| ACM (Polyacrylate) | −15°C to +175°C | Mineral oil, mild chemicals | Automotive, power steering, ATF applications |
| Silicone | −55°C to +180°C | Moderate chemical resistance | High/low temperature extremes where chemical resistance is not critical |
Material Selection Rule of Thumb
- Standard gearbox, pump or motor in normal industrial environment: NBR
- Operating above 120°C or in contact with synthetic lubricants, fuels or solvents: FKM
- Food contact or pharmaceutical duty: PTFE (FDA-compliant grades available)
- If unsure and the media is mineral oil below 120°C: always start with NBR
Decision 3, Size Selection
An oil seal is defined by three dimensions: bore diameter (d) Ã, outer diameter (D) Ã, width (b), all in millimetres. Example: 30Ã, 52Ã, 10 means 30mm bore (shaft size), 52mm OD (housing bore), 10mm wide.
- Measure the shaft diameter (d), this is the bore of the seal
- Measure the housing bore (D), this is the outer diameter of the seal
- Measure the housing depth available (b), this is the seal width
- Cross-reference to SOG catalogue to find the matching designation
Shaft Surface Finish, Critical for Seal Life
The primary lip runs directly on the shaft. Shaft surface finish in the lip contact zone must be Ra 0.2, 0.8 µm (ground finish). Rougher surfaces wear the lip rapidly; smoother surfaces (below Ra 0.2) reduce the oil film the lip needs to function without overheating. A shaft with visible machining marks or rust damage at the seal contact zone will destroy a new seal within weeks.