AS568 standard size, dash -018
AS568-018 O-ring: 0.739 in ID x 0.070 in cross-section
AS568-018 is the AS568 dash 018 O-ring size. It has a 0.739 in (18.77 mm) inside diameter and a 0.070 in (1.78 mm) cross-section, which gives a 0.879 in (22.33 mm) outside diameter as a reference. AS568 controls the inside diameter and the cross-section; the outside diameter is derived.
- Inside diameter
- 0.739 in18.77 mm, +/- 0.009 in
- Cross-section
- 0.070 in1.78 mm, +/- 0.003 in
- Outside diameter
- 0.879 in22.33 mm, reference
- Series
- 0xx0.070 in nominal cord
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Specifications
| Dimension | Value | Tolerance |
|---|---|---|
| Inside diameter (ID) | 0.739 in 18.77 mm | +/- 0.009 in |
| Cross-section (W) | 0.070 in 1.78 mm | +/- 0.003 in |
| Outside diameter (reference) | 0.879 in 22.33 mm | derived: ID + 2 x W |
| Standard | AS568 (SAE Aerospace Standard) | inch authoritative |
Millimeter values are converted. Groove dimensions, squeeze and material engineering follow the gland guidance below and the compound sheet.
Cross-reference
Mil-spec and AMS callouts for AS568-018
AS568-018 is the dash number the military, SAE and NAS part standards below use for this same size. The document sets the compound; the dash sets the dimensions.
| Designator | Document | Compound | Status | Back-up ring |
|---|---|---|---|---|
| MS28775-018 | MIL-PRF-25732 (MS28775 part drawing); now SAE AS28775 | NBR | Inactive (MIL-PRF-25732); AS28775A current (2025) | MS28774-018 |
| M83461/1-018 | MIL-P-83461/1; now SAE AS83461/1 | NBR | Canceled (MIL-P-83461/1); AS83461/1C current (2021) | MS28774-018 |
| M83248/1-018 | MIL-R-83248/1 (Class 1); now SAE AS83248/1 (AMS7276) | FKM | Canceled (MIL-R-83248/1); AS83248/1A current (2021) | MS28774-018 |
| M83248/2-018 | MIL-R-83248/2 (Class 2); now SAE AS3581 (AMS7259) | FKM | Canceled (MIL-R-83248/2); AS3581A current (2020) | MS28774-018 |
| AS3209-018 | SAE AS3209 (AMS7276) | FKM | AS3209C current (2021) | MS28774-018 |
| M83485/1-018 | MIL-R-83485; now SAE AMS-R-83485 | FKM, low-temperature grade | Canceled (MIL-R-83485); AMSR83485A current (2014) | MS28774-018 |
| M25988/1-018 | MIL-DTL-25988/1; now SAE AMS-R-25988 | FVMQ | Active (MIL-DTL-25988/1); AMSR25988B current (2023) | MS28774-018 |
| M25988/2-018 | MIL-DTL-25988/2; now SAE AMS-R-25988 | FVMQ | Active (MIL-DTL-25988/2); AMSR25988B current (2023) | MS28774-018 |
| M25988/3-018 | MIL-DTL-25988/3; now SAE AMS-R-25988 | FVMQ | Active (MIL-DTL-25988/3); AMSR25988B current (2023) | MS28774-018 |
| M25988/4-018 | MIL-DTL-25988/4; now SAE AMS-R-25988 | FVMQ | Active (MIL-DTL-25988/4); AMSR25988B current (2023) | MS28774-018 |
| MS29513-018 | MIL-P-5315 (MS29513 part drawing); now SAE AS29513 (AMS-P-5315) | NBR | Canceled (MIL-P-5315); AS29513C current (2021) | MS28774-018 |
| NAS1611-018 | NAS1613 (AIA) via the NAS1611 part standard | EPDM | status not verified here | MS28774-018 |
| AS3582-018 | SAE AS3582 (AMS3304) | VMQ silicone | AS3582 current (2018) | MS28774-018 |
| AS9386-018 | SAE AS9386 (AMS7267) | VMQ silicone | AS9386B current (2021) | MS28774-018 |
| 4018 | X-ring on the AS568 size (the 4 prefix plus the dash) | any compound | numbering convention | see drawing |
Document statuses are read from DLA ASSIST and SAE Mobilus (read 2026-09-24). This table carries no durometer; the document sets it.
To quote it, send the designator exactly as the print reads, with its revision and any suffix letter. Parts are supplied against the document named and quoted in the compound the print calls out. MS28774-018 is the single-turn scarf-cut PTFE back-up ring on this dash and MS27595-018 the solid one, both under SAE AS8791; the double-turn MS28782 rings run their own numbering, so send that number as printed.
- MIL-P-25732 and MIL-DTL-25732 are older prefixes of the same document; SAE AMS-P-25732 is the parallel material specification.
- M83485/1 is a low-temperature fluorocarbon, not a fluorosilicone; manufacturers now build the part to AMS7287.
- The M25988 slash sheet carries the class and grade; the base document carries the qualification list.
- Manufacturer cross-references flag MS29513 and MS29512 sizes over 0.500 in ID as tighter than AS568 tolerance; the drawing governs.
- An A suffix on a NAS1611 or NAS1612 number is used by manufacturers for a compound qualified to NAS1613 Revision 6; sizes over 0.500 in ID run tighter than AS568 tolerance.
- MS9068 is cross-referenced to AMS3304 by manufacturers; its document status is not verified here.
- The 4 prefix plus the AS568 dash is the X-ring numbering convention; availability by dash is the maker's list.
Gland design
Groove guidance for a 0.070 in cross-section
| Seal type | Squeeze % | Groove width in | Groove depth in | Gland fill % | Convention |
|---|---|---|---|---|---|
| Static face seal, internal pressure | 19 to 32 | 0.101 to 0.107 | 0.050 to 0.054 | 60 to 85 | AS568 industrial (handbook/MIL lineage) |
| Static face seal, external pressure | 19 to 32 | 0.101 to 0.107 | 0.050 to 0.054 | 60 to 85 | AS568 industrial (handbook/MIL lineage) |
| Static radial, piston | 22 to 32 | 0.093 to 0.098 | 0.050 to 0.052 | 60 to 85 | AS568 industrial (handbook/MIL lineage) |
| Static radial, rod | 22 to 32 | 0.093 to 0.098 | 0.050 to 0.052 | 60 to 85 | AS568 industrial (handbook/MIL lineage) |
| Dynamic reciprocating, piston | 15 to 25 | 0.093 to 0.098 | 0.055 to 0.057 | 60 to 85 | AS568 industrial (handbook/MIL lineage) |
| Dynamic reciprocating, rod | 15 to 25 | 0.093 to 0.098 | 0.055 to 0.057 | 60 to 85 | AS568 industrial (handbook/MIL lineage) |
| Rotary | 0 to 10 | 0.080 | 0.065 to 0.066 | 60 to 85 | manufacturer guideline |
| Dovetail face | 27 | 0.055 to 0.059 | 0.050 to 0.052 | 60 to 85 | manufacturer guideline |
| Half dovetail face | see guide | see guide | see guide | 60 to 85 | manufacturer guideline |
Above 1500 psi the published guidance adds anti-extrusion rings (SAE AS4716: one or two above 1500 psi). These are guideline figures, not the standard's text; the groove design guide walks through the choices.
Sources for the table: ERIKS nv, O-ring Technical Handbook, chapter 12 'O-ring Gland Design' (read 2026-09-06); Conquest Seal's own legacy groove-design table (read 2026-09-06); Marco Sealing Solutions, Understanding O-Ring Squeeze, Stretch & Compression (read 2026-09-06); Precision Associates, Inc., Application Data - Seal Gland Design, copyright 2006, 2011 (read 2026-09-06); Trelleborg Sealing Solutions, O-Rings and Back-up Rings, edition June 2024 (read 2026-09-06); Parker® O-Ring Handbook ORD 5700, section 3.7, for the gland fill column (read 2026-09-24).
Compounds for an AS568-018 O-ring
| Family | Standard range | Typical media |
|---|---|---|
| Viton® (FKM) | -26 C to 204 C | fuels, oils, heat |
| Buna-N (NBR) | -34 C to 100 C | mineral oils, hydraulic fluid |
| EPDM (EPDM) | -57 C to 150 C | water, steam, glycol; never petroleum oils |
| Silicone (VMQ) | -54 C to 204 C | dry heat and cold, static service |
| FFKM (FFKM) | -26 C to 320 C | aggressive chemistry and temperature beyond FKM |
| HNBR (HNBR) | -32 C to 149 C | oil with heat |
| Fluorosilicone (FVMQ) | -73 C to 177 C | fuels at low temperature |
| Polyurethane (AU/EU) | -40 C to 82 C | abrasion and high pressure |
| Aflas® (FEPM) | -9 C to 232 C | steam, amines, sour gas |
| Butyl (IIR) | -59 C to 121 C | gas impermeability, brake fluid and phosphate esters; never oil |
| Polyacrylate (ACM) | -21 C to 177 C | hot transmission oil; poor at low temperature and in water |
| Ethylene-acrylic (AEM) | -40 C to 149 C | 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 |
The compound sheet sets the limit for a specific grade. The butyl, polyacrylate and ethylene-acrylic ranges are the handbook's section 2.2 figures (Parker ORD 5700, read 2026-09-14); SBR, natural rubber and epichlorohydrin have no range on file. Name the compound your drawing calls out and we quote AS568-018 in it.
Viton® is a trademark of The Chemours Company; Aflas® is a trademark of AGC; Parker® is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Frequently asked
What are the dimensions of an AS568-018 O-ring?
AS568-018 has a 0.739 in (18.77 mm) inside diameter with a 0.070 in (1.78 mm) cross-section, which gives a 0.879 in (22.33 mm) outside diameter as a reference. AS568 controls the inside diameter and the cross-section; the outside diameter is derived.
What tolerance applies to AS568-018?
The inside diameter carries plus or minus 0.009 in (0.23 mm) and the cross-section plus or minus 0.003 in (0.08 mm). Both come from the AS568 table for this dash number.
Which compounds is AS568-018 available in?
The compound your drawing or specification calls out. The families below show published ranges; the compound sheet sets the limit. Send the compound and we quote the size in it.
Which mil-spec part numbers share the AS568-018 size?
MS28775-018, M83461/1-018, M83248/1-018, M83248/2-018, AS3209-018, M83485/1-018, M25988/1-018, M25988/2-018, M25988/3-018, M25988/4-018, MS29513-018, NAS1611-018, AS3582-018, AS9386-018 all call out the AS568-018 dimensions; each document sets its own compound and hardness class. The X-ring on this size is numbered 4018. Send the designator exactly as the print reads and we quote against that document.
Need AS568-018 in a specific compound or quantity?
Send the part number, the material and the quantity. A Conquest representative reads every request and replies within one business day.
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