AS568 O-Ring Size Chart: Dash Numbers, ID/OD & Cross-Section

Need to filter sizes fast? Use the interactive AS568 O-ring size chart tool — search any dash number and toggle between inches and millimeters, or embed it on your own engineering resources page.

The AS568 O-ring size chart is the reference every buyer, engineer, and maintenance planner reaches for when specifying inch-series O-rings. Published by SAE International as SAE AS568 (originally an aerospace standard, now the dominant U.S. inch O-ring designation), it assigns a simple three-digit “dash number” to each combination of inside diameter (ID) and cross-section (CS). This guide explains how the system works and provides a practical AS568 dash-number size table you can use for quoting, cross-referencing, and reordering.

What Is the AS568 Standard?

AS568 defines O-ring sizes by dash number rather than by raw dimensions. A dash number such as -214 or -110 uniquely identifies one nominal ID and one cross-section. This lets procurement, engineering, and suppliers speak the same language across the FKM, NBR, EPDM, and silicone compounds an application may require. The standard covers dash -001 through -475 across five standard cross-sections.

How Dash Numbers Work

The leading digit(s) of the dash number set the cross-section series; the remaining digits step through inside diameters within that series:

• -0XX → 0.070 in cross-section (1.78 mm)
• -1XX → 0.103 in cross-section (2.62 mm)
• -2XX → 0.139 in cross-section (3.53 mm)
• -3XX → 0.210 in cross-section (5.33 mm)
• -4XX → 0.275 in cross-section (6.99 mm)

Three special sizes (-001, -002, -003) sit below the 0.070 in cord at 0.040–0.060 in and have no ISO 3601 metric counterpart.

How to Read the Dimensions

Every AS568 size has three nominal dimensions:

• ID (Inside Diameter) – the controlled, sealing dimension.
• CS (Cross-Section / cord diameter) – the round cross-section of the ring.
• OD (Outside Diameter) – always equals ID + 2 × CS.

Values below are in inches (nominal) with millimeter equivalents. Always design to groove, not to the free O-ring, and allow for AS568 tolerances (±0.003 in on the 0.070 in cord, scaling up with cord size).

AS568 O-Ring Size Chart (Common Dash Numbers)

The table groups the most-specified dash numbers by cross-section. For sizes outside this list (full range to -475), contact us with the dash number or groove dimensions.

Choosing the Right Material for the Size

The dash number fixes geometry; the compound fixes performance. Pair any AS568 size with the elastomer your service environment demands:

• FKM (Viton®) – chemical, fuel, and heat resistance to ~205 °C; see our FKM temperature range guide.
• NBR (Buna-N) – oil and fuel resistance at low cost.
• EPDM – weather, ozone, and steam resistance.
• Silicone (VMQ) / FVMQ – wide temperature and food/medical grades; see material specification library.
• FFKM – extreme chemical and temperature service.

Standard, Custom, and Non-Standard O-Rings

AS568 covers standard sizes, but many applications need a non-standard ID, a special cross-section, or a bonded/configured seal. Anlintech molds AS568-sized O-rings in FKM, NBR, EPDM, silicone, HNBR, and FFKM, and can produce custom cross-sections or custom rubber O-rings to your drawing. Send the dash number (or groove ID/OD/CS) plus compound and quantity for a quote; we ship with material certification and dimensional reports.

Related Guides

• Shore A Hardness Guide — how durometer affects sealing, compression and wear.
• Compression Set in Rubber Seals — what it is, how it is tested, and how to keep set low.
• Rubber Stoppers — materials, solid vs holed, and custom sizing.
• Rubber Bellows & Boots — material and convolution design for custom boots.

Interactive O-Ring Size Chart Tools

• AS568 O-Ring Size Chart Tool (SAE dash numbers)
• ISO 3601 O-Ring Size Chart Tool (Metric)
• JIS B2401 O-Ring Size Chart Tool (G-type)
• Embed Our O-Ring Size Charts (Free, Attribution-Only)