NF T47-501 is the French national standard for metric O-ring dimensions, used across hydraulic, pneumatic, automotive, agricultural, and industrial sealing in France, Belgium, North Africa, and francophone markets. Because it is closely aligned with ISO 3601 and DIN 3771, NF T47-501 sizes are functionally interchangeable with most European metric O-rings.
This guide gives engineers and buyers a practical reference for NF T47-501 sizes, tolerance classes, groove design, material selection, inspection, and international cross-references.
Short Answer: NF T47-501 at a Glance
| Attribute | NF T47-501 |
|---|---|
| System | Metric inside diameter × cross-section |
| Cross sections | 1.00 mm to 8.00 mm |
| Common sizes | 3.00 × 1.00 up to 200.00 × 8.00 mm |
| Primary markets | France, Belgium, North Africa, francophone aerospace and public works |
| Tolerance bands | ±0.08 mm to ±0.18 mm on CS; ±0.14 mm to ±0.56 mm on ID |
| Closest equivalents | ISO 3601 A/B/C/D/E series; DIN 3771 metric sizes |
NF T47-501 uses ID × CS notation, so a size is written as 25.00 × 3.00 mm. The standard covers dimensions and tolerances only; material and hardness are specified separately.
What Is NF T47-501?
NF T47-501 is the French O-ring dimensional standard published by AFNOR. It defines metric O-ring sizes for static and dynamic sealing in hydraulic, pneumatic, automotive and industrial applications. The standard is the default O-ring specification on French OEM drawings, public-works contracts, and aerospace ground-support equipment.
Unlike AS568, which uses dash numbers, NF T47-501 identifies each O-ring by its inside diameter (ID) and cross-sectional diameter (CS) in millimetres. It matches metric drawings directly.
Key facts:
- NF T47-501 specifies dimensions and tolerances only.
- It is broadly compatible with ISO 3601-1 and DIN 3771, simplifying pan-European sourcing.
- Sizes are written as ID × CS (e.g., 20.00 × 2.65 mm).
Scope and Structure
NF T47-501 organises O-rings around four elements:
- Cross-sectional diameters — the ring thickness that determines compression set and pressure capability.
- Inside diameters — the free-state inner diameter that defines gland fit.
- Tolerances — allowable variation in ID and CS based on ring size.
- Gland design guidance — groove depth, width, and compression percentage for static, dynamic, and rotary service.
Because the standard does not specify materials, engineers pair it with an elastomer callout such as NBR 70 Shore A, FKM 75 Shore A, or EPDM 70 Shore A based on fluid and temperature requirements.
NF T47-501 Cross-Sectional Series
NF T47-501 lists 21 standard cross-sectional diameters. Smaller cross sections suit precision instruments and small-bore fittings; larger cross sections provide the compression reserve needed for high-pressure hydraulics, large flanges, and heavy static seals.
Complete Cross-Section Table
| CS (mm) | Typical Application | International Equivalent |
|---|---|---|
| 1.00 | Precision instruments, small pneumatic fittings | — |
| 1.50 | Miniature hydraulic and medical devices | — |
| 1.60 | European small-bore sensors and valves | — |
| 1.78 | Compact seals | AS568 imperial cross section |
| 1.80 | General purpose metric seals | ISO 3601 A-series |
| 2.00 | General purpose static and dynamic seals | — |
| 2.40 | Medium-pressure hydraulic applications | — |
| 2.50 | Pumps and fluid handling equipment | — |
| 2.62 | Industrial and aerospace-compatible | AS568-1xx cross section |
| 2.65 | European hydraulic and pneumatic | ISO 3601 B-series |
| 3.00 | Heavy-duty static seals | — |
| 3.53 | High-pressure hydraulics, flanges | AS568-2xx cross section |
| 3.55 | Industrial metric seals | ISO 3601 C-series |
| 4.00 | Large-bore flanges, industrial valves | — |
| 5.00 | High-pressure hydraulic cylinders | — |
| 5.30 | Heavy static and dynamic seals | ISO 3601 D-series |
| 5.33 | Large industrial and marine | AS568-3xx cross section |
| 6.00 | Marine and large industrial equipment | — |
| 6.99 | Large flanges and pipelines | AS568-4xx cross section |
| 7.00 | Large static seals | ISO 3601 E-series |
| 8.00 | Specialised heavy static sealing | — |
This range covers everything from miniature pneumatic sensors to 250 mm+ flange seals. Many cross sections intentionally match ISO 3601 or AS568 values, so a drawing written in one standard can usually be sourced from stock produced to another.
Dimensional Tolerances
NF T47-501 tolerance bands are grouped by cross-section range and inside-diameter range. Tighter tolerances apply to smaller rings because the same absolute error represents a larger percentage of the dimension. Larger rings receive proportionally wider absolute tolerances to remain manufacturable without excessive tooling cost.
NF T47-501 ID and CS Tolerances
| CS Range (mm) | CS Tolerance | ID Range (mm) | ID Tolerance |
|---|---|---|---|
| 1.00 – 1.60 | ±0.08 | ≤ 10 | ±0.14 |
| 1.00 – 1.60 | ±0.08 | 10 – 20 | ±0.17 |
| 1.78 – 2.65 | ±0.09 | ≤ 13 | ±0.17 |
| 1.78 – 2.65 | ±0.09 | 13 – 30 | ±0.22 |
| 1.78 – 2.65 | ±0.09 | 30 – 50 | ±0.28 |
| 3.00 – 3.55 | ±0.10 | ≤ 20 | ±0.20 |
| 3.00 – 3.55 | ±0.10 | 20 – 40 | ±0.28 |
| 3.00 – 3.55 | ±0.10 | 40 – 85 | ±0.36 |
| 4.00 – 5.33 | ±0.13 | ≤ 40 | ±0.28 |
| 4.00 – 5.33 | ±0.13 | 40 – 80 | ±0.36 |
| 4.00 – 5.33 | ±0.13 | 80 – 140 | ±0.45 |
| 6.00 – 7.00 | ±0.15 | ≤ 80 | ±0.36 |
| 6.00 – 7.00 | ±0.15 | 80 – 160 | ±0.45 |
| 8.00 | ±0.18 | ≤ 120 | ±0.45 |
| 8.00 | ±0.18 | 120 – 250 | ±0.56 |
For a 25.00 × 3.00 mm ring, the 3.00 mm CS falls in the 3.00 – 3.55 mm band and the 25.00 mm ID falls in the 20 – 40 mm range. The acceptable envelope is CS 2.90 – 3.10 mm and ID 24.72 – 25.28 mm.
When designing a groove, use the worst-case combination of ID and CS tolerance to verify minimum squeeze and maximum groove fill. Our compression calculator can check these values for any NF T47-501 size.
Groove Design for NF T47-501
NF T47-501 is a dimensional standard and does not publish a standalone gland design document. French engineers typically use ISO 3601 or DIN 3771 groove design principles.
Static Grooves
- Groove width ≈ 1.15 × CS
- Target compression: 15 – 25% of cross-sectional diameter
- Shallower grooves increase squeeze and sealing contact stress
Dynamic Grooves
- Groove width ≈ 1.2 – 1.3 × CS
- Target compression: 10 – 15% to minimise friction and stick-slip
- Use harder compounds (80 – 90 Shore A) for high-pressure dynamic service
Rotary Grooves
- Limit groove fill to 75 – 80% maximum
- Use harder grades (80 – 90 Shore A) and heat-resistant materials such as FKM or HNBR
Squeeze is calculated as (CS − groove depth) / CS × 100. For a 3.00 mm CS O-ring in a 2.55 mm deep groove, squeeze = 15%, suitable for static service.
NF T47-501 vs ISO 3601 and DIN 3771
NF T47-501, ISO 3601, and DIN 3771 are metric standards with substantial overlap, but verify exact dimensions for critical applications.
| Standard | Region | Identification | Relationship to NF T47-501 |
|---|---|---|---|
| NF T47-501 | France / francophone markets | ID × CS (mm) | French national standard |
| ISO 3601 | International | ID × CS (mm) | A/B/C/D/E series map directly to NF T47-501 |
| DIN 3771 | Germany / EU | ID × CS (mm) | Functionally equivalent to NF T47-501 |
| SMS 1588 | Sweden | ID × CS (mm) | Shares same cross sections and ID ranges |
| JIS B 2401 | Japan | ID × CS (mm) | P/G/S/V series are metric-compatible |
| AS568 | USA | Dash number | Imperial cross sections convert to nearest metric NF sizes |
A French drawing calling for 25.00 × 3.00 mm NF T47-501 can usually be sourced as ISO 3601 or DIN 3771 25.00 × 3.00 mm with no functional difference. Include tight tolerance bands and material certifications on the purchase order rather than assuming supplier defaults.
Common NF T47-501 Size Examples
The following table shows representative NF T47-501 sizes from miniature instrumentation to large industrial static seals, written as ID × CS (mm).
| ID (mm) | CS (mm) | Size (ID × CS) | Typical Application |
|---|---|---|---|
| 3.00 | 1.00 | 3.00 × 1.00 | Precision instruments |
| 5.00 | 1.50 | 5.00 × 1.50 | Small pneumatic fittings |
| 7.00 | 1.80 | 7.00 × 1.80 | Compact hydraulic fittings |
| 10.00 | 2.00 | 10.00 × 2.00 | General machinery seals |
| 15.00 | 2.50 | 15.00 × 2.50 | Pump and valve housings |
| 20.00 | 2.65 | 20.00 × 2.65 | Hydraulic cylinders |
| 25.00 | 3.00 | 25.00 × 3.00 | Medium-pressure systems |
| 30.00 | 3.55 | 30.00 × 3.55 | Industrial flange seals |
| 40.00 | 4.00 | 40.00 × 4.00 | Large static seals |
| 50.00 | 5.00 | 50.00 × 5.00 | Heavy equipment hydraulics |
| 80.00 | 5.30 | 80.00 × 5.30 | Large bore hydraulics |
| 100.00 | 6.00 | 100.00 × 6.00 | Marine and offshore |
| 150.00 | 7.00 | 150.00 × 7.00 | Large industrial tanks |
| 200.00 | 8.00 | 200.00 × 8.00 | Specialised static sealing |
The full NF T47-501 size chart contains the complete range of available sizes and tolerances.
Material Selection for NF T47-501 O-Rings
NF T47-501 defines geometry, not material. The engineer selects the elastomer based on fluid compatibility, temperature, pressure, and motion type.
| Material | Hardness | Strengths | Typical Application |
|---|---|---|---|
| NBR | 70/90 Shore A | Mineral oils, hydraulic fluids, fuels | General hydraulic and pneumatic |
| FKM | 75/90 Shore A | High temperature, fuels, aromatics | Aerospace ground support, automotive |
| EPDM | 70 Shore A | Water, steam, phosphate esters, ozone | Water systems, outdoor equipment |
| VMQ (Silicone) | 70 Shore A | Low temperature, food-grade | Food machinery, medical devices |
| HNBR | 80 Shore A | High temperature, sour gas, ozone | Oilfield, automotive, high-pressure |
| PTFE / FFKM | — | Aggressive chemicals, extreme temperatures | Chemical processing, semiconductor |
For French aerospace or automotive specifications, include the compound callout alongside the NF T47-501 size, such as NBR per ASTM D2000 5AA510 or FKM per AMS-R-83485.
Inspection and Acceptance Criteria
NF T47-501 O-rings are inspected for dimensional conformance and visual quality at room temperature (23 ± 2 °C).
Dimensional Inspection
- Inside diameter: measured with optical comparator, cone gauge, or precision bore gauge within tolerance.
- Cross-sectional diameter: measured at three points around the circumference within tolerance.
- Out-of-roundness: checked at multiple positions for large rings.
Visual Acceptance
- Flash within geometric tolerance and no interference with groove seating.
- No porosity, blisters, voids, cracks, tears, cuts, or foreign inclusions visible under normal inspection.
- Surface texture uniform; mould marks acceptable only if they do not reduce cross section below tolerance minimum.
Batch Testing
For critical batches, typical tests include hardness (ASTM D2240 / ISO 48), tensile strength and elongation (ASTM D412 / ISO 37), compression set, and fluid swell when required.
FAQ
Q1: Is NF T47-501 the same as ISO 3601?
They are closely aligned but not identical. NF T47-501 is the French national standard; ISO 3601 is international. Most cross sections and size ranges overlap, making them interchangeable in practice. For critical applications, specify the exact standard and request a conformance certificate.
Q2: What industries use NF T47-501 O-rings?
French automotive, aerospace ground support, agricultural machinery, public works, hydraulics, pneumatics, and marine equipment in francophone markets. It is also common on equipment exported to francophone markets.
Q3: How is an NF T47-501 size written?
Sizes are written as inside diameter × cross-section in millimetres. For example, 25.00 × 3.00 mm means ID 25.00 mm and CS 3.00 mm. There are no dash numbers as in AS568.
Q4: Can I use an ISO 3601 O-ring in an NF T47-501 groove?
Usually yes. The two standards share the same metric size grid, so an ISO 3601 ring of the same nominal ID × CS will fit an NF T47-501 gland. Verify actual dimensions and tolerances for high-pressure or high-precision applications, and use our compression calculator to confirm squeeze and fill.
Q5: What tolerance applies to a 20.00 × 2.65 mm NF T47-501 O-ring?
A 2.65 mm CS falls in the 1.78 – 2.65 mm band (±0.09 mm). A 20.00 mm ID falls in the 13 – 30 mm range (±0.22 mm). The acceptable envelope is CS 2.56 – 2.74 mm and ID 19.78 – 20.22 mm.
Q6: Does NF T47-501 specify material or hardness?
No. NF T47-501 covers dimensions and tolerances only. The engineer must specify the elastomer, hardness, colour, and any material certifications separately.
Q7: What is the largest NF T47-501 cross section?
The largest standard cross section is 8.00 mm, typically paired with IDs up to 250 mm. For diameters above the standard table, custom cord-spliced or vulcanised rings can be manufactured to the same cross section.
Q8: Can you supply NF T47-501 O-rings with material certifications?
Yes. We provide batch certificates, material test reports, and full traceability for NBR, FKM, EPDM, HNBR, VMQ, and PTFE NF T47-501 O-rings. Certificates can include hardness, tensile strength, elongation, compression set, and fluid-swelling results on request.
---
Need NF T47-501 O-rings for a French specification or export project? Request a quote with the size (ID × CS), material, hardness, quantity, and certification requirements. We manufacture standard NF T47-501 sizes and custom dimensions to order, with fast delivery to France, Belgium, North Africa, and global industrial customers. For technical questions, contact our engineering team.