Learn more about encapsulated O-rings including materials, applications, and performance characteristics here:
Encapsulated O-ring tolerances differ significantly from molded elastomer O-rings. These components are manufactured using a cut-to-length and welding process, introducing dimensional variability governed by material behavior, thermal expansion, and measurement methodology.
Understanding these differences is critical when specifying encapsulated seals for high-performance applications.
The Reality of Encapsulated O-Ring Tolerances
FEP SILICONE O-RING
Encapsulated O-rings are not molded components. They are produced by forming fluoropolymer tubing around an elastomer core and joining the material to create a continuous seal. This process results in tolerances that are derived from length-based calculations rather than mold-defined geometry.
As a result, applying AS568 molded O-ring tolerances to encapsulated products often leads to unrealistic expectations and unnecessary rejection of functional parts.
Material properties further influence dimensional behavior. FEP and PFA exhibit significantly higher coefficients of thermal expansion compared to metals and molded elastomers. Even small temperature variations can produce measurable dimensional changes.
Additionally, encapsulated O-rings may exhibit slight ovality prior to installation due to residual stress from forming and handling. Once installed, the sealing forces restore functional geometry.
Measurement Considerations
- Radial measurements alone may not reflect true functional geometry
- Axial compression affects final installed dimensions
- Measurement equipment and technique influence results
- Environmental conditions impact dimensional readings
These factors must be considered when evaluating encapsulated O-ring performance and dimensional compliance.
RMA vs AS568 Tolerances
Encapsulated O-rings follow RMA (Rubber Manufacturers Association) tolerance classes, typically L1 or L2. These tolerances are based on cut-length variation and converted to inside diameter values using geometric relationships.
AS568 standards apply specifically to molded elastomer O-rings and are not directly applicable to encapsulated sealing products.
Practical Engineering Expectations
What Sets M-COR Apart? Transparency in manufacturing Reality
Claims of extremely tight inside diameter tolerances—particularly on larger FEP or PFA encapsulated O-rings—often ignore fundamental material behavior. While tighter groupings can be achieved through post-production sorting, these are not representative of standard manufacturing tolerances.
Aligning tolerance expectations with engineering reality ensures proper sealing performance and reduces unnecessary inspection discrepancies.
M-Cor Approach to Tolerance Transparency
At M-Cor, we take a data-driven approach to encapsulated sealing solutions. Each part is measured, documented, and evaluated using precision inspection systems. We provide customers with clear guidance on tolerance expectations and application-specific performance.
This approach allows engineers to specify components with confidence, avoiding the uncertainty often associated with encapsulated sealing solutions.
Access Detailed Tolerance Data
Detailed tolerance charts, dimensional data, and application-specific guidance are available upon request. These resources include expanded RMA-based tolerance ranges and real measurement data for encapsulated O-rings.
To access full tolerance documentation, please request access below. Password Required.
Request Access to Full Tolerance Charts
Related Resource
For a complete overview of materials, applications, and performance characteristics, visit our main encapsulated O-ring page. Encapsulated O-Rings Overview
Frequently Asked Questions
Do encapsulated O-rings meet AS568 tolerances?
No. Encapsulated O-rings follow RMA-based tolerances due to their cut-to-length manufacturing process.
Why do dimensional measurements vary?
Material flexibility, thermal expansion, measurement method, and environmental conditions all influence dimensional readings.
Can tighter tolerances be achieved?
Tighter groupings can be achieved through statistical sorting, but these are not considered standard manufacturing tolerances.