Viton FKM O-Rings: AS568 Dash Sizes and Durometer Explained
By Mutual Screw & Supply | Published: 2026-10-24
Category: Buying Guides
Understand Viton FKM o-ring dash sizes, durometer ratings, and how to choose between 60 and 75 Shore A for your application.
Quick answer
AS568 dash numbers define the inner diameter and cross-section of Viton FKM o-rings. Durometer (Shore A) measures hardness, affecting compression and sealing force.
Why dash size and durometer both matter
Dash size alone doesn't tell you how the o-ring will perform under pressure or temperature. Two o-rings with the same AS568 dash number can feel very different if one is 60 Shore A and the other is 75 Shore A. The softer 60 durometer seals with less gland fill but may extrude under high pressure. The harder 75 durometer resists extrusion but needs more clamping force.
Temperature range is the same for both materials listed here (-15°F to +400°F), so your choice comes down to pressure, gland design, and any special requirements like FDA compliance or color coding.
Frequently asked questions
- What does an AS568 dash number mean?
- Each dash number corresponds to a specific inner diameter and cross-section. For example, AS568-222 has a 1.484" ID and 0.139" cross-section. The dash number is a standardized way to identify o-ring dimensions without listing inches or millimeters.
- What is the difference between 60 and 75 durometer Viton?
- 60 Shore A is softer and compresses more easily, which helps seal low-pressure or uneven gaps. 75 Shore A is harder, resists extrusion under high pressure, and holds its shape better in dynamic applications. Both have the same temperature range. Choose 60 durometer for low-pressure static seals and 75 durometer for higher-pressure or dynamic sealing.
- Can I use a black Viton o-ring in food contact?
- Not all black Viton o-rings are FDA compliant. The black 75 durometer AS568-235 is not listed as FDA compliant. If you need food-grade material, look for white or specifically marked FDA-compliant o-rings like the 60 durometer white AS568-222. Always verify FDA compliance on the product spec sheet before using in food contact.
- How do I measure an o-ring to find its dash size?
- Measure the inner diameter and cross-section (thickness) in inches. Then match those dimensions to an AS568 dash size chart. For example, a 1.484" ID with a 0.139" cross-section corresponds to dash 222. Use calipers for accuracy; o-rings can deform, so take multiple readings.
Product facts
- 0.139" CS X 1.484" ID Viton FKM O-Rings | AS568-222 | Dash 222 | FDA Compliant | 60 Durometer | White (20 / Pkg.): AS568-222, 1.484" ID, 0.139" cross-section, 60 Shore A, white, FDA compliant The white color and FDA compliance make this a good fit for food-contact or visually inspected seals where material purity matters.
0.139" CS X 1.484" ID Viton FKM O-Rings | AS568-222 | Dash 222 | FDA Compliant | 60 Durometer | White (20 / Pkg.) - 0.139" CS X 3.109" ID Viton FKM O-Rings | AS568-235 | Dash 235 | 75 Durometer | Black (20 / Pkg.): AS568-235, 3.109" ID, 0.139" cross-section, 75 Shore A, black The larger 3.109" ID suits bigger shaft or piston applications, and the 75 durometer provides better extrusion resistance under higher system pressures.
0.139" CS X 3.109" ID Viton FKM O-Rings | AS568-235 | Dash 235 | 75 Durometer | Black (20 / Pkg.)
