Silicone vs Viton O-Rings: AS568-405 and Dash 106 Compared

These two o-rings are not the same size — start there

The silicone vs Viton o-ring question usually hides a more basic decision: which material survives your temperature and chemical exposure. But before you compare elastomers, confirm the o-ring actually fits your groove. The two catalog parts in this comparison are different dash sizes, so they are not drop-in substitutes for each other.

The silicone part is AS568-405, a 70 Shore A red o-ring sold 13 per package. The Viton FKM part is AS568-106, a 75 Shore A brown o-ring with a 0.174 in inner diameter and 0.103 in cross-section, sold 500 per package. Use each part's own dimensions to check fit; do not assume one dash size can replace another.

Size and pack-count facts that affect the decision

• Silicone O-Rings | AS568-405 | Dash 405 | FDA Compliant | 70 Durometer | Red (13 / Pkg.): AS568-405 dash size, 70 Shore A durometer, red silicone, 13 per package. The dash size sets the groove fit; the 70 Shore A durometer is the silicone baseline you are comparing against.

  

• 0.103" CS X 0.174" ID Viton FKM O-Rings | AS568-106 | Dash 106 | 75 Durometer | Brown (500 / Pkg.): AS568-106 dash size, 0.174 in (4.42 mm) inner diameter, 0.103 in (2.62 mm) cross-section, 75 Shore A durometer, 500 per package. These are the actual dimensions you must match to your hardware; the 500-piece pack suits repeat assembly or inventory, not a one-off repair.

  

Temperature range is the clearest material split

The silicone AS568-405 o-ring carries a service range of -80°F to +450°F (-62°C to +232°C). The Viton FKM AS568-106 o-ring carries a service range of -15°F to +400°F (-26°C to +204°C). If your application runs cold, silicone has the wider low-end window. If it runs hot but not beyond 400°F, both materials are rated in that range, so temperature alone may not decide it.

Do not read these ranges as a complete chemical compatibility guide. The supplied records give temperature limits and material names, not a fluid-by-fluid resistance chart. For aggressive solvents, fuels, or acids, confirm compatibility with the o-ring manufacturer or a compatibility reference before installing either material.

Temperature and compliance evidence from the catalog

• Silicone O-Rings | AS568-405 | Dash 405 | FDA Compliant | 70 Durometer | Red (13 / Pkg.): Service range -80°F to +450°F (-62°C to +232°C); FDA 21 CFR 177.2600 compliant. The wide low-temperature range and FDA compliance make this silicone part relevant to cold service and food-contact questions.
• 0.103" CS X 0.174" ID Viton FKM O-Rings | AS568-106 | Dash 106 | 75 Durometer | Brown (500 / Pkg.): Service range -15°F to +400°F (-26°C to +204°C); no FDA compliance is stated in the supplied record. The narrower low end and the absence of a stated FDA claim mean you should not assume this Viton part for food-contact service without verification.

70 durometer vs 75 durometer: a small number with real consequences

Durometer measures hardness on the Shore A scale. The silicone AS568-405 is 70 Shore A; the Viton FKM AS568-106 is 75 Shore A. That five-point gap is modest, but it can matter in low-pressure sealing, where a softer ring conforms more easily, or in extrusion-prone joints, where a harder ring resists deformation better.

The supplied records do not include compression-set data, tensile strength, or recommended squeeze percentages. Do not choose between 70 and 75 Shore A based on durometer alone; use the groove design and the seal manufacturer's engineering guidance to set squeeze and hardware tolerances.

• Silicone AS568-405 at 70 Shore A: Softer of the two. Consider when the groove and mating surfaces need more conformability and temperatures stay within the silicone range.
• Viton FKM AS568-106 at 75 Shore A: Slightly harder. Consider when the joint sees higher pressure or when FKM's fluid resistance is the deciding factor, provided temperature stays within -15°F to +400°F.

FDA compliance changes the food-contact answer

Only the silicone AS568-405 is listed as compliant with FDA 21 CFR 177.2600 in the supplied records. If you are searching for FDA compliant o-rings for food equipment, that is a concrete, citable claim for the silicone part. The Viton FKM AS568-106 record does not state FDA compliance, so you should not treat it as food-contact rated without confirming the specific compound and documentation.

FDA compliance is not the same as suitability for every food process. Cleaning chemicals, fats, and operating temperature still affect service life. Use the compliance status as a starting filter, then verify the full application with the seal supplier.

How to choose between these two catalog o-rings

• Match the dash size first: AS568-405 and AS568-106 are different sizes. Measure your groove and confirm the dash size before comparing materials.
• Check the cold end of the temperature range: Silicone reaches -80°F; Viton FKM reaches -15°F. If cold flexibility matters, silicone is the safer starting point based on the supplied ranges.
• Check the hot end against your process: Silicone is rated to +450°F and Viton FKM to +400°F. Stay within the material's stated range and confirm chemical compatibility separately.
• Use FDA status only where it is documented: The silicone AS568-405 carries FDA 21 CFR 177.2600 compliance in the record; the Viton FKM AS568-106 does not state it.
• Buy the pack size that matches your work: The silicone part comes 13 per package; the Viton FKM part comes 500 per package. A prototype and a production run have different pack-size economics.

What the catalog does not tell you

Neither supplied record includes chemical resistance charts, pressure ratings, or installation instructions. That absence is a limitation of the evidence here, not proof that the manufacturer provides none. Before you commit either o-ring to a critical seal, request the compound datasheet and confirm compatibility with the actual media, pressure, and hardware surface finish.

For straightforward replacement work within the stated temperature ranges, the choice often comes down to size, FDA status, and pack quantity. For chemical service or safety-critical joints, treat this comparison as a shortlist and verify the details with the supplier.