— O-Rings & Seals
AS568 Standard O-Ring Sizing
AS568 (SAE Aerospace Standard 568) is the standard US O-ring size chart. Every size is defined by ID (inside diameter) and CS (cross-section diameter), related by OD = ID + (2 × CS). The "dash number" is a lookup code, not a raw dimension — the leading digit(s) select a cross-section series, and numbers are not continuous across series.
| Series (Dash Range) | Cross-Section (CS) |
|---|---|
| 000s (-001 to -050) | 0.070 in (1.78 mm) |
| 100s (-102 to -178) | 0.103 in (2.62 mm) |
| 200s (-201 to -284) | 0.139 in (3.53 mm) |
| 300s (-309 to -395) | 0.210 in (5.33 mm) |
| 400s (-425 to -475) | 0.275 in (6.99 mm) |
Representative AS568 Sizes
| Dash # | Series | ID (in) | CS (in) | OD (in) |
|---|---|---|---|---|
| -002 | 000 | 0.042 | 0.050 | 0.142 |
| -004 | 000 | 0.070 | 0.070 | 0.210 |
| -010 | 000 | 0.239 | 0.070 | 0.379 |
| -014 | 000 | 0.489 | 0.070 | 0.629 |
| -110 | 100 | 0.362 | 0.103 | 0.568 |
| -114 | 100 | 0.612 | 0.103 | 0.818 |
| -210 | 200 | 0.734 | 0.139 | 1.012 |
| -214 | 200 | 0.984 | 0.139 | 1.262 |
| -216 | 200 | 1.109 | 0.139 | 1.387 |
| -325 | 300 | 1.475 | 0.210 | 1.895 |
| -425 | 400 | 4.475 | 0.275 | 5.025 |
O-Ring Material Comparison
| Material | Temp. Range | Hardness (Shore A) | Compatibility Notes |
|---|---|---|---|
| Nitrile/Buna-N (NBR) | -40°F to 250°F | 50–90 (70 common) | Good with petroleum oils/fuels; poor ozone/UV/weathering, poor with ketones and brake fluid |
| Fluorocarbon (FKM/Viton) | -15°F to 400°F+ | 60–90 (75 common) | Excellent heat, fuel, oil, ozone/chemical resistance; poor with ketones, amines, steam, brake fluid |
| EPDM | -65°F to 300°F | 40–90 | Excellent with brake fluid, steam, hot water, ozone/weathering; poor — swells — with petroleum oils/fuels |
| Silicone (VMQ) | -100°F to 500°F | 30–80 | Excellent weathering/ozone, food/medical-safe grades, widest temp range; poor tear/abrasion strength, poor with oils/fuels |
| Neoprene (CR) | -67°F to 250°F | 40–80 | Good with refrigerants/ammonia; poor with gasoline and brake fluid |
| PTFE | -300°F to 500°F | ~95–98 (near-rigid) | Outstanding broad chemical resistance, lowest friction; can't stretch over sharp edges — used as encapsulation/flange-seal material rather than a stretch-fit O-ring |
Seal Types Beyond O-Rings
| Seal Type | Static/Dynamic | Typical Application |
|---|---|---|
| O-ring | Both | Cheapest, simplest — static flange/port seals and low-to-moderate-speed dynamic seals (pistons, valves, cylinders) |
| Lip seal / rotary shaft seal | Dynamic (rotary) | Retains lubricant in and excludes contaminants from rotating shafts — engine/gearbox/pump shafts |
| Face seal / mechanical seal | Dynamic (rotary), fixed + rotating face pair | Pump shafts and rotating equipment handling process fluid, where pressure/temp exceeds lip-seal capability |
| Gasket | Static | Flat or formed flange-joint seal relying on compressive clamp force; not for moving parts |
| Quad-ring / X-ring | Dynamic (also static) | Four-lobed cross-section resists twist/roll better than an O-ring — lower friction, longer wear life in reciprocating/rotating applications |