Common oil seal sizes
Seal sizes follow the shaft, and for a given shaft there are usually only two or three standard bore and width combinations. If the shaft is a standard metric size, the seal almost certainly exists off the shelf.
| Shaft | Common sizes |
|---|---|
| 15 mm | 15x26x7, 15x30x7, 15x35x7 |
| 20 mm | 20x32x7, 20x35x7, 20x40x7 |
| 25 mm | 25x40x7, 25x42x7, 25x47x7 |
| 30 mm | 30x42x7, 30x47x7, 30x52x7 |
| 35 mm | 35x47x7, 35x52x7, 35x55x8 |
| 40 mm | 40x55x8, 40x62x8, 40x72x10 |
| 45 mm | 45x62x8, 45x65x8, 45x72x10 |
| 50 mm | 50x65x8, 50x72x8, 50x80x10 |
| 55 mm | 55x72x8, 55x80x10, 55x85x10 |
| 60 mm | 60x80x10, 60x85x10, 60x90x10 |
Seal type codes
The type code describes the lip arrangement and the casing. It matters because a single-lip seal in a dusty application will fail early, and a double-lip seal adds drag that a light-duty drive may not want.
| Code | Construction | Use |
|---|---|---|
| TC / TG4 | Double lip, rubber covered, spring loaded | General purpose with dust exclusion |
| TB / SC | Single lip, rubber covered, spring loaded | Clean environments |
| TA / SB | Single lip, metal outer, spring loaded | Tight housings, better press fit |
| SA | Single lip, no spring | Grease retention only, low pressure |
| V-ring | Axial elastomer ring on the shaft | Secondary dust exclusion |
Seal material and temperature
The compound decides temperature and fluid compatibility, and getting it wrong is the usual cause of a seal that fails within weeks. Nitrile is the default and is fine for mineral oil and grease at moderate temperature. Viton handles heat and aggressive fluids at several times the price.
Shaft condition matters as much as the seal. A shaft with a wear groove from the previous seal will chew a new one; fit a speedi-sleeve or move the seal axially so the lip runs on fresh metal.
| Material | Temperature range | Suits |
|---|---|---|
| Nitrile (NBR) | -40 to 120 °C | Mineral oil, grease, water |
| Viton (FKM) | -20 to 200 °C | Hot oil, fuels, many chemicals |
| Silicone (VMQ) | -60 to 180 °C | Dry heat, low shaft speed |
| PTFE | -60 to 200 °C | Chemicals, dry running, high speed |
| Polyacrylate (ACM) | -20 to 150 °C | Transmission and engine oils |
