Always shaft first
The three numbers are the shaft diameter, the housing bore and the width, in that order: 25x40x7 fits a 25 mm shaft in a 40 mm bore and is 7 mm wide.
Reference tool — not a selection
Read an oil seal before it goes in an RFQ.
Oil seal
Shaft, bore, width.
Type the marking. Pick the type if it is not marked. Put an offered replacement in the second field, and the reader checks the sizes, the type and the lip material. The section and the RFQ line update with every change.
Type, if the marking has none
Units
Examples:
Replacement check
On the markings alone: the maker’s catalogue, the housing and the medium decide.
All 130 engineering tools
An oil seal, a rotary shaft lip seal, is marked with three sizes in one order: shaft diameter, housing bore, width, as in 25x40x7. A type letter (A, AS, B, BS, C, CS) and a lip material (NBR, FKM…) often follow. Type the marking, or three measurements from a worn seal, and the reader names each part, draws the seal in section in its housing and writes the RFQ line.
Makers’ codes such as TC, SC or BASL mean different things from maker to maker, so the reader keeps them as printed. The seal and machine documentation still decide.
How a marking is read
Three sizes, a letter, a material.
The outside decides the housing
A is rubber-covered outside, B has an open metal case, C a closed metal case with an inner case. A metal outside needs a precisely machined, clean bore.
S adds a dust lip
AS, BS and CS have a second, outer lip that keeps dirt away from the sealing lip; the sealing lip faces the oil.
| Type | Outside | Lips |
|---|---|---|
| A | rubber-covered | sealing lip |
| AS | rubber-covered | sealing lip and dust lip |
| B | open metal case | sealing lip |
| BS | open metal case | sealing lip and dust lip |
| C | closed metal case with an inner case | sealing lip |
| CS | closed metal case with an inner case | sealing lip and dust lip |
| Code | Material | Also written | What the sources say |
|---|---|---|---|
| NBR | Nitrile rubber | — | The usual lip material for oils and greases |
| FKM | Fluorocarbon rubber | FPM, Viton | For higher temperatures and more demanding media |
| HNBR | Hydrogenated nitrile rubber | H-NBR | — |
| ACM | Polyacrylate rubber | — | — |
| VMQ | Silicone rubber | MVQ | — |
| PTFE | PTFE | — | Usually a special design |
Makers’ codes (TC, SC, TB, SB, BA, BASL, HMS5, CRW1 and others) are not in the table: suppliers read the same letters differently, so they go into the request as printed, next to the size.
Sources
Size order and type letters: the German Wikipedia article "Radialwellendichtring" (its example DIN 3760-AS90x110x10-NBR), the dicht.de glossary entry "DIN 3760", JIOrings’ article on DIN 3760, DIN 3761 and ISO 6194, and SKF type A listings that give d1, d2 and b in the same order. All three describe A, B and C the same way (rubber-covered, open metal case, closed or reinforced metal case) and S as the added dust lip; JIOrings places B and C under DIN 3761 while the other two list all six under DIN 3760, so the reader names the letters without a standard number. Lip materials: dicht.de and the same Wikipedia article.
Before you send the seal
Questions about oil seals in an RFQ
What does 25x40x7 mean on an oil seal?
A 25 mm shaft, a 40 mm housing bore and a 7 mm width, always in that order. The difference between bore and shaft, 15 mm, halved, is the 7.5 mm radial section the seal fills.
What is the difference between A, B and C?
The outside. A is rubber-covered, B has an open metal case, C a closed metal case with an inner case. A metal outside needs a precisely machined, clean housing bore. An S after the letter adds a dust lip.
What do TC, SC or BASL mean?
They are makers’ type codes, and suppliers read the same letters differently. Put the code in the request as printed, with the size, and describe the seal: rubber or metal outside, one lip or two.
What should the request include?
The marking as printed, or the shaft, bore and width measured; the type and the lip material; the machine, the position and the oil; and photographs of the old seal from both sides. An inch seal is quoted in inches, since its sizes fall between whole millimetres.
Marking read?
Send the line with the photographs.
A decoded marking is a cross-check, not proof. Attach photographs of the seal from both sides, and Vessel Core checks it against the machine documentation before an offer goes back.
Buyer tools
