Inputs
Results are guidance. Measured O-ring diameters carry ±1–2% tolerance, and groove dimensions follow the manufacturer catalog. Material advice is based on general compatibility; check the manufacturer chemical resistance chart for specific fluids and additives.
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O-ring: the inside diameter and cross-section you enter are matched to the nearest AS568 inch-series number. The ISO 3601 metric size (d1 × d2) is shown as well; cross-sections are 1.78 / 2.62 / 3.53 / 5.33 / 6.99 mm.
Oil seal: the DIN 3760 size code is written d × D × b. Shaft surface speed is the basis for material choice and the permitted speed.
d1 [mm] = inside diameter [inch] × 25.4 (AS568 number matched to size)
v [m/s] = π × d [mm] × n [rpm] ÷ 60,000
Order code: type d × D × b material (e.g. AS 40×62×8 NBR)
Worked example
Example: ID 18.64 mm, cross-section 3.53 mm → AS568-210 (18.64 × 3.53). Shaft Ø40, bore Ø62, width 8 mm, 1500 rpm → 3.1 m/s; for mineral oil at 80 °C NBR is suitable: AS 40×62×8 NBR.
Practical tips
- Measure an O-ring free, with inside diameter and cross-section taken separately; do not stretch it.
- In dynamic service squeeze and groove finish decide life; it is sized differently from a static groove.
- The seal shaft should be hardened and finely ground (Ra 0.2–0.8 µm).
- A standard seal tolerates roughly 0.5 bar; above that choose a pressure seal or PTFE.
Frequently asked questions
What is AS568?
A US O-ring size standard that assigns dash numbers (e.g. -210) to inside diameter and cross-section.
AS568 versus ISO 3601?
AS568 is an inch series and ISO 3601 a metric one; cross-sections are close but inside diameters are not always identical.
What do oil seal types A, AS, B, BS mean?
DIN 3760 letters: S is a dust lip, A a metal case and B a rubber-covered outer surface.
Which material when?
NBR is the economical choice for oil and air; FKM for heat and chemicals; EPDM for water, steam and brake fluid.
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