O-rings
Spliced and vulcanized O-rings
A spliced and vulcanized O-ring is made from extruded cord stock cut to length and joined at the ends, either heat vulcanized or cold bonded with an adhesive, which gives any inside diameter without mold tooling and makes it the usual route for a large-diameter or non-standard static seal. Spliced and vulcanized rings are supplied to order in every O-ring compound family that is made as cord, quoted from the diameter, the cord cross-section and the compound.
- Made from
- Cord stockextruded, cut to length
- Joint
- Heat vulcanizedor cold bonded in the field
- Tooling
- NoneApple Rubber lists rings to 500 in ID
- Service
- Staticquoted for static duty only
Spliced cord or a molded endless ring
A molded O-ring comes out of a mold made for that one size, which is why the standard lists stop where the tooling stops: the largest AS568 O-ring size is dash -475, a 25.94 in inside diameter. A spliced ring starts from a length of extruded cord, so the diameter is set by the cut length; Apple Rubber lists thermobonded rings from 2 in to 500 in inside diameter and beyond.
The trade is the joint. A spliced joint is the weak point of the ring, so Conquest Seal quotes spliced O-rings for static service, in face seals, covers, doors and flanges, and not for moving rods or pistons. At volume, and wherever the seal moves, a molded ring wins, and a non-standard size in a dynamic application is quoted as a custom molded ring.
| Feature | Spliced and vulcanized | Molded endless |
|---|---|---|
| Made from | extruded cord stock, cut and joined | a mold for that size |
| Tooling | none (Apple Rubber) | one mold per size and cross-section |
| Diameter range | set by the cut length; Apple Rubber lists 2 in to 500 in ID | the tooled sizes; the largest AS568 ID is 25.94 in at dash -475 |
| Service | static; a moving seal is quoted molded | static and dynamic |
| Weak point | the joint | the parting line on the sealing diameter |
| Best for | oversize and odd inside diameters, low quantity | standard sizes, volume, moving seals |
How the splice is made: hot vulcanized or cold bonded
Two joints are in use. In a hot vulcanized splice the cord ends are joined and the joint is cured under heat and pressure, so the two ends become one piece; Trelleborg catalogs round cord rings made by butt jointing extruded cord and vulcanizing the joint, and Apple Rubber's thermobonding molds the joint with its own adhesives and cures it. In a cold bonded splice the cut ends are joined with an adhesive and no heat, which is the joint a field splicing kit makes.
The Parker® O-Ring Handbook defines the two bond types: a cold bond joins already-vulcanized elastomer with a contact cement, and a vulcanized bond uses heat and pressure to cure the elastomer against the other member at the same time. Rings supplied to order are made with the hot joint; the cold joint is for a repair on the machine while the vulcanized ring is on its way.
| Method | How it works | Typical use | Limits |
|---|---|---|---|
| Hot (heat) vulcanized splice | Cord ends joined and the joint cured under heat and pressure, so the ends become one piece (Parker glossary, vulcanized bond; Trelleborg butt vulcanized round cord rings). | Static seals supplied ready to install: covers, flanges, doors and tank lids; the standard way a spliced ring is supplied to order. | Quoted for static service; a moving seal is quoted molded. |
| Cold bonded (adhesive) splice | Already-cured cord ends joined with a contact cement, no heat (Parker glossary, cold bond). | Field repair and in-place fabrication from a splicing kit, when a machine has to run before the hot-spliced ring arrives. | Static only. |
| Molded endless ring | Cured as one piece in a mold cut for that size and cross-section; no joint. | Standard sizes, moving seals, volume. | One mold per size; the size lists end where the tooling ends (AS568 at dash -475). |
When each is used
Choose a spliced ring when the inside diameter is larger than the molded lists reach, when the size is non-standard and the quantity is small, or when a cover or flange needs a static seal and tooling a mold makes no sense. Choose a molded ring when the seal moves, when the size is a standard one, or when the quantity justifies the mold.
If the print calls out a standard dash number, send that; every AS568 size has its own page and the size chart lists them all. If it gives a diameter that no list reaches, send the diameter and Conquest Seal quotes it spliced.
Cord cross-sections
Cord stock is extruded in the standard O-ring cross-sections, so a spliced ring is normally specified on one of the AS568 cords or the matching ISO 3601-1 metric cords. The five AS568 cords are tabulated here with their metric equivalents. Beyond them Apple Rubber lists cord from 0.070 in to 1 in for its thermobonded rings.
| Series | Dash range | W in | W mm | W tolerance in | Sizes |
|---|---|---|---|---|---|
| 0xx series | -004 to -050 (-001 to -003 run 0.040, 0.050 and 0.060 in) | 0.070 | 1.78 | +/- 0.003 | 47 |
| 1xx series | -102 to -178 | 0.103 | 2.62 | +/- 0.003 | 77 |
| 2xx series | -201 to -284 | 0.139 | 3.53 | +/- 0.004 | 84 |
| 3xx series | -309 to -395 | 0.210 | 5.33 | +/- 0.005 | 87 |
| 4xx series | -425 to -475 | 0.275 | 6.99 | +/- 0.006 | 51 |
The ISO 3601-1 metric cord series sits within tolerance of the AS568 cords on the same rows, so a metric print is quoted on the same cord. Other cord diameters are quoted case by case.
Which materials can be spliced
The compilation that follows names, family by family, whether a manufacturer cited here names the family for a spliced or thermobonded ring, and says so where none does. A family no source names is quoted case by case, because the cord has to exist in that compound and cross-section before it can be cut. Every family here has its own material page under O-ring materials.
| Family | ASTM D1418 | What the sources state |
|---|---|---|
| Nitrile (Buna-N) | NBR | Named by Apple Rubber for thermobonded rings. |
| Viton® (FKM) | FKM | Named by Apple Rubber for thermobonded rings. |
| EPDM | EPDM | Not named by the manufacturers cited here; quoted case by case against cord availability. |
| Silicone | VMQ | Named by Apple Rubber for thermobonded rings. |
| Fluorosilicone | FVMQ | Named by Apple Rubber for thermobonded rings. |
| HNBR | HNBR | Not named by the manufacturers cited here; quoted case by case against cord availability. |
| FFKM | FFKM | Not named by the manufacturers cited here; quoted case by case against the compound maker's cord availability. |
| Polyurethane | AU/EU | Not named by the manufacturers cited here; quoted case by case against cord availability. |
| PTFE | PTFE | Not listed as cord or as a spliced ring by the manufacturers cited here. Send the size and it is quoted against what the PTFE maker can supply. |
| Aflas® | FEPM | Not named by the manufacturers cited here; quoted case by case against cord availability. |
Manufacturer lists change; availability of a given family and hardness as cord is confirmed at quote.
Service ranges of the compound families
Spliced rings are quoted in the standard compound families, and the media and the temperature decide which. The ranges are the Parker O-Ring Handbook family ranges, with makers' printed figures for SBR, natural rubber and epichlorohydrin; the compound sheet governs a specific grade.
| Family | ASTM D1418 | Standard range, C | Typical media |
|---|---|---|---|
| Viton | FKM | -26 to 204 | fuels, oils, heat |
| Buna-N | NBR | -34 to 100 | mineral oils, hydraulic fluid |
| EPDM | EPDM | -57 to 150 | water, steam, glycol; never petroleum oils |
| Silicone | VMQ | -54 to 204 | dry heat and cold, static service |
| FFKM | FFKM | -26 to 320 | aggressive chemistry and temperature beyond FKM (FFKM vs FKM) |
| HNBR | HNBR | -32 to 149 | oil with heat |
| Fluorosilicone | FVMQ | -73 to 177 | fuels at low temperature |
| Polyurethane | AU/EU | -40 to 82 | abrasion and high pressure |
| Aflas | FEPM | -9 to 232 | steam, amines and sour gas; poor at low temperature |
| Butyl | IIR | -59 to 121 | gas impermeability, brake fluid and phosphate esters; never oil |
| Polyacrylate | ACM | -21 to 177 | hot transmission oil; poor at low temperature and in water |
| Ethylene-acrylic | AEM | -40 to 149 | hot automotive oil |
| SBR | SBR | -46 to 100 | the compound sheet governs |
| Natural rubber | NR | -50 to 70 | the compound sheet governs |
| Epichlorohydrin | ECO | -40 to 135 | the compound sheet governs |
Larger and non-standard sizes: what to send
An O-ring larger than the molded lists reach, or on a non-standard diameter, is supplied to order as a spliced and vulcanized ring in any compound family made as cord. A spliced ring is quoted from five things, and a drawing replaces all of them if you have one.
- The inside diameter or the outside diameter, and which one you mean.
- The cord cross-section, in inches or millimeters, or the profile if it is not round.
- The compound and hardness as your print names them.
- The quantity.
- The application: what it seals, the pressure, and whether anything moves against it, since a moving seal is quoted molded instead.
Related pages
Frequently asked
What is a vulcanized O-ring?
An O-ring made from a length of extruded cord stock whose two ends are joined and cured closed under heat and pressure, instead of being molded as an endless ring. The result is a ring of any diameter with no mold tooling behind it.
What is the difference between a hot vulcanized splice and a cold bonded splice?
A hot splice cures the joint under heat and pressure, so the ends become one piece. A cold splice joins the already-cured ends with an adhesive and no heat; the Parker O-Ring Handbook calls the two a vulcanized bond and a cold bond. Rings supplied to order are made with the hot joint, and the cold joint is for a repair in the field.
What is the difference between a spliced O-ring and a molded O-ring?
A molded ring is formed endless in a mold made for that size, so it is limited to the tooled sizes but has no joint and can run on a moving surface. A spliced ring is cut from cord and joined, so it can be any diameter but its joint is the weak point and it is used in static service.
Can a spliced O-ring be used in dynamic service?
No. The joint is the weak point, so Conquest Seal quotes spliced rings for static service only. A moving rod or piston takes a molded ring, or an X-ring where the stroke is long, and a non-standard dynamic size is quoted as a custom molded ring.
How large can a spliced O-ring be?
Apple Rubber lists thermobonded rings to 500 in inside diameter and beyond. For comparison, the largest AS568 molded size, dash -475, is 25.94 in inside diameter; a spliced ring is the usual answer beyond that and for any odd diameter in between.
Which materials can be spliced?
Apple Rubber names nitrile, FKM, silicone and fluorosilicone for its thermobonded rings. EPDM, HNBR, polyurethane, Aflas and FFKM are quoted case by case against cord availability, and PTFE is not listed as cord by the manufacturers cited here.
Which cross-sections are available as cord?
The standard O-ring cords: the five AS568 cross-sections from 0.070 in to 0.275 in and the matching ISO 3601-1 metric cords from 1.8 to 7.0 mm. Apple Rubber lists cord to 1 in (25.4 mm) for thermobonded rings; other cord diameters and profiles are quoted case by case.
What do I send to get a spliced O-ring quoted?
The inside or outside diameter and which one it is, the cord cross-section or profile, the compound and hardness, the quantity, and what the ring seals. A drawing covers all of it.
Related guides
Sources
[S1] Apple Rubber, MacrOrings and Thermobonding pages: 50.8 to 12,700 mm ID, 1.78 to 25.4 mm cross-section, tolerance statement against slash-and-glue - https://www.applerubber.com/products/macrorings/ and https://www.applerubber.com/services/thermobonding/ - accessed 2026-09-14; [S2] Parker O-Ring Handbook ORD 5700, section 10 glossary: cold bond, vulcanized bond and butt joint definitions; Trelleborg Sealing Solutions, O-Rings and Back-up Rings, June 2024, section D.7 Round cord rings (butt vulcanized); Parker O-Ring Handbook ORD 5700, 2021 printing, section IX, AS568 size tables, pages 9-2 to 9-11, read 2026-09-27; Precision Polymer Engineering, ISO 3601 O-ring Sizes reference table, https://www.prepol.com/documents/o-ring-sizes-iso3601/, read 2026-09-06; Parker O-Ring Handbook ORD 5700, 2021 printing, section IX, AS568 size tables, pages 9-2 to 9-11, read 2026-09-27; Parker O-Ring Handbook ORD 5700 compound family ranges. Dimensional facts are stated in our own words; no standard's text or table is reproduced.
Viton is a trademark of The Chemours Company. No affiliation or endorsement is implied.
Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Aflas is a trademark of AGC. No affiliation or endorsement is implied.
Apple Rubber is a trademark of its owner; no affiliation or endorsement is implied.
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Send the diameter, the cord and the compound
ID or OD and which one, the cross-section, the compound and the quantity, or the drawing. A Conquest representative replies with the quote. Quotes answered within one business day. A person answers (714) 632-9830, Pacific business hours.
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