AS568 standard size, dash -918
AS568-918 O-ring: 1.355 in ID x 0.116 in cross-section
AS568-918 is the AS568 dash 918 O-ring size. It has a 1.355 in (34.42 mm) inside diameter and a 0.116 in (2.95 mm) cross-section, which gives a 1.587 in (40.32 mm) outside diameter as a reference. AS568 controls the inside diameter and the cross-section; the outside diameter is derived.
- Inside diameter
- 1.355 in34.42 mm, +/- 0.012 in
- Cross-section
- 0.116 in2.95 mm, +/- 0.004 in
- Outside diameter
- 1.587 in40.32 mm, reference
- Series
- 9xx bossstraight-thread tube fitting seal
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Specifications
| Dimension | Value | Tolerance |
|---|---|---|
| Inside diameter (ID) | 1.355 in 34.42 mm | +/- 0.012 in |
| Cross-section (W) | 0.116 in 2.95 mm | +/- 0.004 in |
| Outside diameter (reference) | 1.587 in 40.32 mm | derived: ID + 2 x W |
| Standard | AS568 (SAE Aerospace Standard) | inch authoritative |
Millimeter values are converted. Port and groove dimensions follow the boss fitting standard on your drawing and the compound sheet.
Cross-reference
Mil-spec and AMS callouts for AS568-918
AS568-918 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 |
|---|---|---|---|---|
| M83461/2-18 | MIL-P-83461 (boss sheet /2); now SAE AMS-P-83461/2 | NBR | Canceled (base document MIL-P-83461); AMSP83461 issued (1998) | see drawing |
| AS3208-18 | SAE AS3208 (AMS7276) | FKM | AS3208A current (2020) | see drawing |
| MS29512-18 | MIL-P-5315 (MS29512 boss drawing); now SAE AS29512 (AMS-P-5315) | NBR | Canceled (MIL-P-5315); AS29512C current (2021) | see drawing |
| NAS1612-18 | NAS1613 (AIA) via the NAS1612 boss standard | EPDM | status not verified here | see drawing |
| AS9385-18 | SAE AS9385 (AMS7267) | VMQ silicone | AS9385A current (2020) | 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.
- 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.
- One manufacturer now lists the boss sizes under AS9386-9YY; SAE revised AS9385 to A in 2020, so both numbers are quoted as printed.
Compounds for an AS568-918 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 AS568-918 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 AS568-918 O-ring?
AS568-918 has a 1.355 in (34.42 mm) inside diameter with a 0.116 in (2.95 mm) cross-section, which gives a 1.587 in (40.32 mm) outside diameter as a reference. AS568 controls the inside diameter and the cross-section; the outside diameter is derived.
What tolerance applies to AS568-918?
The inside diameter carries plus or minus 0.012 in (0.30 mm) and the cross-section plus or minus 0.004 in (0.10 mm). Both come from the AS568 table for this dash number.
Which compounds is AS568-918 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 AS568-918 size?
M83461/2-18, AS3208-18, MS29512-18, NAS1612-18, AS9385-18 all call out the AS568-918 dimensions; each document sets its own compound and hardness class. Send the designator exactly as the print reads and we quote against that document.
Need AS568-918 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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