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 a butt or scarfed joint, either heat vulcanized in a small mold 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
- Noneno upper limit on diameter
- Service
- Staticevery source restricts the spliced ring to static duty
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; ERIKS states there is no upper limit to diameter, and 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 spliced O-rings are used in static service, in face seals, covers, doors and flanges, and not on moving rods or pistons. At volume, and wherever the seal moves, a molded ring wins; Global O-Ring states that a non-standard size in a dynamic application is made as a custom molded ring instead.
| Feature | Spliced and vulcanized | Molded endless |
|---|---|---|
| Made from | extruded cord stock, cut and joined | a mold for that size |
| Tooling | none (Apple Rubber, ERIKS) | one mold per size and cross-section |
| Diameter range | no upper limit (ERIKS); the smallest ring depends on the cord cross-section | the tooled sizes; the largest AS568 ID is 25.94 in at dash -475 |
| Service | static (Global O-Ring, ESP); not where the ring may roll (ERIKS) | static and dynamic |
| Weak point | the joint | the parting line on the sealing diameter |
| Surface | as extruded, no flash line (ERIKS) | a parting line, flash trimmed |
| 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, and the manufacturers describe them the same way. In a hot vulcanized splice the cord ends are cut square or scarfed at 45 degrees, an uncured bonding compound is applied, and the joint cures under heat and pressure in a small mold, so the two ends cross-link into one piece; Global O-Ring, ESP International and ERIKS each describe that heated joint, and Apple Rubber's thermobonding cures a heat-activated adhesive the same way. In a cold bonded splice the cord ends are cut square in a jig, a rapid-set adhesive goes on one face, and the ends are pressed together for about thirty seconds with no heat, which is the joint a field splicing kit makes.
The Parker® O-Ring Handbook defines the two bond types the same way: 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 per the cited source |
|---|---|---|---|
| Hot (heat) vulcanized splice | Ends cut square or scarfed at 45 degrees; an uncured bonding compound is applied and the joint is cured under heat and pressure in a small mold, so the ends cross-link into one piece (Global O-Ring, ESP, ERIKS). | Static seals supplied ready to install: covers, flanges, doors, tank lids and weather seals; the standard way a spliced ring is supplied to order. | Static service (Global O-Ring, ESP). ERIKS lists three restrictions: dynamic duty where the ring may roll, heavy stretching of low-strength compounds, and small diameters at high volume where a molded ring is the better buy. ERIKS states its scarfed joints reach in some cases 90 percent of cord strength; Global O-Ring pull-tests samples to failure. |
| Cold bonded (adhesive) splice | Ends cut square in a jig; a rapid-set adhesive on one face; the ends held together under finger pressure for about thirty seconds, no heat (Global O-Ring splicing kits). | Field repair and in-place fabrication from a splicing kit, when a machine has to run before the hot-spliced ring arrives. | Static only (Global O-Ring). The same kit maker states that a hot spliced vulcanized ring is the better seal for static service and that excess adhesive weakens the bond; Apple Rubber notes that a cyanoacrylate glue leaves a harder spot at the joint. |
| 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). |
Apple Rubber calls its heat-cured joint thermobonding and states that other companies' cyanoacrylate glues create a harder formation at the bond point; that is a hot splice by another name, and the comparison is theirs, not a figure on this page.
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. Apple Rubber puts it as weather seals and large inside diameters that do not see much dynamic force. 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 the manufacturers list wider ranges: ERIKS makes hot vulcanized rings from 1.78 mm to 25.4 mm cross-section, Apple Rubber from 0.070 in to 1 in, and Marco Rubber stocks round cord from 0.039 in to 2.000 in; Global O-Ring also vulcanizes square and X-profile cord. The smallest inside diameter a spliced ring can be made in depends on the cross-section, so a thick cord needs a larger minimum ring (ERIKS).
| 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
ESP International states that any standard O-ring material or compound can be vulcanized; the compilation that follows names, family by family, which manufacturers name the family for a spliced or vulcanized 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 as a vulcanized ring material by Global O-Ring, ERIKS (60, 75 and 90 Shore A) and Apple Rubber; ESP stocks nitrile cord for vulcanizing; Marco lists nitrile cord and splicing kits. |
| Viton® (FKM) | FKM | Named by Global O-Ring, ERIKS (Viton A, GF, GLT and GFLT grades) and Apple Rubber; ESP stocks FKM cord for vulcanizing; Marco lists FKM cord and splicing kits. |
| EPDM | EPDM | Named by Global O-Ring and ERIKS; Marco lists EPDM cord and splicing kits. |
| Silicone | VMQ | Named by Global O-Ring, ERIKS and Apple Rubber; Marco lists silicone cord. |
| Fluorosilicone | FVMQ | Named by Global O-Ring, ERIKS and Apple Rubber; Marco lists fluorosilicone cord. |
| HNBR | HNBR | Named by ERIKS (75 Shore A); Global O-Ring stocks HNBR cord and vulcanizes rings from its stock cord. Not named by Apple Rubber, ESP or Marco. |
| FFKM | FFKM | Not named by any of the sources; covered only by ESP's general statement. Quoted case by case against the compound maker's cord availability. |
| Polyurethane | AU/EU | Named by ERIKS (75 Shore A); Marco lists polyurethane cord. Not named by Global O-Ring, Apple Rubber or ESP. |
| PTFE | PTFE | Not listed as cord or as a spliced ring by any of the sources. Send the size and it is quoted against what the PTFE maker can supply. |
| Aflas® | FEPM | Named by Global O-Ring and ERIKS (70 and 90 Shore A); Marco lists Aflas cord. |
Manufacturer lists change; availability of a given family and hardness as cord is confirmed at quote. Neoprene, butyl and sponge cords are also listed by the sources and are quoted the same way.
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; 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 |
| 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 | no range on file | the compound sheet governs |
| Natural rubber | NR | no range on file | the compound sheet governs |
| Epichlorohydrin | ECO | no range on file | 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 square or X.
- 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 at a butt or scarfed joint 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 applies an uncured bonding compound to the cut ends and cures the joint under heat and pressure in a small mold, so the ends cross-link into one piece. A cold splice joins the cut ends with a rapid-set adhesive and finger pressure, no heat. Global O-Ring states the hot spliced vulcanized ring is the better seal for static service and sells the cold kit for repairs in the field.
Is a spliced joint as strong as the cord?
The manufacturers state it in their own terms: ERIKS says its 45 degree scarfed hot joints reach in some cases 90 percent of cord strength and tests joint samples to breakage, and Global O-Ring pull-tests samples of its vulcanized rings to failure. No figure on this page is a Conquest Seal test result.
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. Global O-Ring and ESP state static service, and ERIKS lists dynamic duty where the ring may roll as a restriction. A moving rod or piston takes a molded ring, or an X-ring where the stroke is long; Global O-Ring makes a non-standard dynamic size as a custom molded ring.
How large can a spliced O-ring be?
ERIKS states there is no upper limit to diameter, and 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?
Nitrile, FKM, EPDM, silicone, fluorosilicone, HNBR, polyurethane and Aflas are each named as cord or as a vulcanized ring material by at least one of the manufacturers cited on this page. FFKM is covered only by ESP's general statement that any standard compound can be vulcanized, and PTFE is not listed as cord by any of them; both are quoted case by case.
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. The manufacturers list wider ranges, ERIKS to 25.4 mm and Marco to 2.000 in, and square and X profiles; other cord diameters 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] Global O-Ring and Seal, Vulcanized O-Rings: heated-mold joint, butt and 45 degree bevel cuts, static use, custom molded for dynamic, materials, profiles, pull tests - https://www.globaloring.com/vulcanized-rings/ - accessed 2026-09-14; [S2] Global O-Ring and Seal, O-Ring Splicing Kits: rapid-set adhesive, thirty seconds, static only, hot spliced ring as the better option - https://www.globaloring.com/o-ring-splicing-kits/ - accessed 2026-09-14; [S3] Global O-Ring and Seal, Cord Stock: HNBR cord, vulcanized by the maker from its own cord - https://www.globaloring.com/cord/ - accessed 2026-09-14; [S4] ERIKS Technical Handbook O-rings, section 16 Vulc-O-rings and O-ring Cords: 45 degree scarf, joint tensile testing, 1.78 to 25.4 mm, no upper diameter limit, smallest ID by cross-section, restrictions, materials - https://o-ring.info/en/o-ring/Oring-Handbook/ERIKS_SealingElements_TechnicalHandbook_O-rings_VulcOring-Cord.pdf - accessed 2026-09-14; [S5] Apple Rubber, Why Cord Stock Is Critical to Thermobonded O-Rings (2020-01-28): heat-cured adhesive vs cyanoacrylate, weather seals and low dynamic force, 2 to 500 in ID, 0.070 to 1 in cord, materials, no mold - https://www.applerubber.com/hot-topics-for-engineers/why-cord-stock-is-critical-to-thermobonded-o-rings/ - accessed 2026-09-14; [S6] 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; [S7] ESP International, Vulcanization Calculator: bonding agent heated at the joint, any standard compound, not for dynamic applications or large quantities, cord sizes - https://www.espint.com/vulcanized-o-rings - accessed 2026-09-14; [S8] Marco Rubber, O-Ring Cord and O-Ring Splicing Kits: round cord 0.039 to 2.000 in, materials, 40 to 90 durometer, kit contents - https://www.marcorubber.com/o-ring-cord.htm and https://www.marcorubber.com/o-ring-splicing-kit.htm - accessed 2026-09-14; [S9] Parker O-Ring Handbook ORD 5700, section 10 glossary: cold bond, vulcanized bond and butt joint definitions; Cord splice as the no-tooling route, static only; butt-vulcanized cord as a catalog item; AS568 cross-sections and the -475 upper size; ISO 3601-1 metric cords and their overlap with the AS568 cords; 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.
MacrOring is a trademark of its owner; no affiliation or endorsement is implied.
ERIKS is a trademark of its owner; no affiliation or endorsement is implied.
Global O-Ring is a trademark of its owner; no affiliation or endorsement is implied.
ESP International is a trademark of its owner; no affiliation or endorsement is implied.
Marco Rubber is a trademark of its owner; no affiliation or endorsement is implied.
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.
Request a quoteLast updated