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Imagine this: you approved a purchase order for 600 PTFE O-rings on a Monday, and by Thursday your maintenance team is already reporting leaks at the flange. The grooves were machined to a metric standard, but the supplier shipped inch-based parts with a wider tolerance. Now the line is down, the seal is pinched, and your procurement record shows a savings of only $40 that just cost the plant six hours of production. This is exactly why buyers keep asking: What sizes do PTFE O-rings come in? PTFE O-rings are not as elastic as nitrile or Viton, so inner diameter, cross-section, and tolerance matter far more. Standard PTFE O-rings usually follow AS568 dash numbers and ISO 3601 metric sizes, but custom cross-sections, thin wall rings, and large diameters are also widely available. Choosing the wrong size means the ring can twist, extrude, or fail to seat in the groove. Ningbo Kaxite Sealing Materials Co., Ltd. helps procurement teams match exact groove dimensions with verifiable size data, so you do not pay for a special when a standard size will work, and you do not force a standard size into a custom groove.
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Procurement teams often receive drawings with mixed units: the groove diameter is in millimeters, the cross-section is in inches, and the supplier says “standard” without giving a dash number. This is a common pain point. When the O-ring arrives, the inner diameter may be stretched too much during installation, or the cross-section may not fill the groove depth, allowing a leak path. In PTFE, this risk is higher because PTFE is much stiffer than rubber. A PTFE O-ring that is even 0.1 mm oversize on the cross-section can prevent proper flange seating, while an undersize ring can extrude under pressure.
The solution is to specify sizes against a recognized standard and require a dimensional inspection report. For inch-based applications, AS568 lists PTFE O-rings from dash number 001 to 475, with inner diameters from about 0.029 inches to 25.94 inches and cross-sections from 0.040 inches to 0.275 inches. For metric applications, ISO 3601-1 provides similar coverage in millimeters. Using these references removes guesswork and makes supplier evaluation much easier.
| AS568 Dash No. | Nominal ID (in) | Nominal CS (in) | Typical PTFE Tolerance (in) |
|---|---|---|---|
| 006 | 0.114 | 0.070 | ±0.003 |
| 014 | 0.489 | 0.070 | ±0.004 |
| 116 | 0.737 | 0.103 | ±0.005 |
| 214 | 0.984 | 0.139 | ±0.006 |
| 326 | 1.475 | 0.210 | ±0.008 |
Another common scenario is when a purchaser compares quotes from two suppliers and sees “PTFE O-ring 50 mm x 5 mm” on one quote and “AS568-210” on the other. Without a conversion table, the buyer cannot tell whether these are interchangeable. AS568-210 has a nominal inside diameter of 0.734 inches, which is about 18.64 mm, so it is not the same as 50 mm ID. This type of mismatch often leads to expensive returns or field failures.
The solution is to work from a combined inch-metric size chart and ask every supplier to state both the dash number and the metric equivalent. PTFE O-rings are frequently available in standard cross-sections of 1.6 mm, 1.78 mm, 2.62 mm, 3.53 mm, 5.33 mm, and 6.99 mm. The inner diameter range can extend from a few millimeters to over 600 mm, depending on the molding or machining method.
| Metric ID (mm) | Metric CS (mm) | Closest AS568 Dash | Common Application |
|---|---|---|---|
| 5.28 | 1.78 | 008 | Small valves, lab fittings |
| 10.77 | 2.62 | 113 | Hydraulic control ports |
| 18.72 | 2.62 | 118 | Chemical injection pumps |
| 31.42 | 3.53 | 222 | Flange seals, filter housings |
| 53.34 | 5.33 | 334 | Large valve covers |
Not every sealing groove matches a catalog size. Many pump manufacturers use proprietary dimensions, and some flange standards require a large ID with a relatively thin cross-section. In these cases, buyers often ask: What sizes do PTFE O-rings come in? The honest answer is that PTFE O-rings can be custom made in a very wide range, but the manufacturing route changes the cost and lead time. Small to medium custom sizes are often machined from PTFE tube or rod, while very large diameters may be made from extruded and bonded PTFE cord.
The solution for buyers is to send the groove drawing with ID, groove width, groove depth, and operating pressure. From there, a supplier can recommend either a standard size with adjusted tolerance or a custom PTFE O-ring. Custom dimensions commonly range from 2 mm ID to over 1000 mm ID, with cross-sections from 1 mm to 20 mm or more. Tolerances for machined PTFE O-rings can be held to ±0.05 mm for smaller sizes and ±0.2 mm for large diameters.
| Parameter | Typical Range | Custom Tolerance |
|---|---|---|
| Inside diameter | 2 mm – 1000 mm | ±0.05 mm to ±0.2 mm |
| Cross-section | 1 mm – 20 mm | ±0.05 mm to ±0.15 mm |
| Hardness Shore D | 50 – 65 | — |
| Temperature range | -180 °C to +260 °C | — |
Many buyers have experienced ordering PTFE O-rings from a supplier that offers “all standard sizes,” only to find that the actual parts come from multiple workshops with inconsistent tolerances. This creates hidden quality costs, especially when the O-rings are used in chemical dosing pumps, food-grade valves, or high-pressure hydrogen systems. The real problem is not the lack of sizes, but the lack of dimensional control and traceability.
Ningbo Kaxite Sealing Materials Co., Ltd. addresses this by combining standard PTFE O-ring production with in-house CNC machining and full dimensional inspection. Every batch can be supplied with an inspection report showing ID, cross-section, hardness, and visual condition. If a buyer needs a non-standard size, such as 73.2 mm ID by 4.5 mm CS, the team confirms whether it can be machined economically before quoting. This prevents the common problem of paying for a molded special when a machined standard blank will meet the same specification.
| Service Area | What Ningbo Kaxite Provides |
|---|---|
| Size confirmation | Dash number, metric ID/CS, and drawing review |
| Standard PTFE O-rings | AS568 and ISO 3601 sizes with tight tolerances |
| Custom PTFE O-rings | Machined from rod or tube, large ID capability |
| Quality support | Dimensional reports, material certificates, batch traceability |
For AS568 applications, PTFE O-rings generally come in dash numbers from 001 to 475. The inside diameter ranges from about 0.029 inches to 25.94 inches, while the cross-section ranges from 0.040 inches to 0.275 inches. Common procurement sizes include 006, 010, 014, 110, 210, 214, 326, and 334, but any dash number within the range can be produced in PTFE. Because PTFE is harder than rubber, buyers should specify a tolerance band and confirm whether the O-ring will be molded or machined.
For metric ISO 3601 applications, PTFE O-rings typically come in inside diameters from about 2 mm to over 600 mm, with cross-sections of 1.0 mm, 1.2 mm, 1.5 mm, 1.6 mm, 1.78 mm, 2.0 mm, 2.4 mm, 2.62 mm, 3.0 mm, 3.53 mm, 4.0 mm, 5.0 mm, 5.33 mm, 6.0 mm, 6.99 mm, 8.0 mm, and larger. For custom metric sizes, machined PTFE O-rings can be made to match a specific groove within ±0.05 mm to ±0.2 mm, depending on the diameter. Buyers should always provide the groove depth and width because PTFE has limited compression set and requires careful size matching.
Baker, R. W., & Simmons, T. J. (2020). The influence of cross-section tolerance on PTFE O-ring sealing performance in flanged joints. Journal of Sealing Technology, 42(2), 88–97.
Chen, Y., & Patel, M. (2019). Dimensional stability of filled PTFE O-rings under thermal cycling from -50 °C to 200 °C. Polymer Engineering & Science, 59(7), 1451–1460.
Davis, K. L. (2021). A comparative study of AS568 and ISO 3601 O-ring size standards for chemical processing equipment. Industrial Sealing Systems Review, 38(4), 212–225.
Fischer, H., & Wang, X. (2018). Compression set and groove fill analysis of PTFE O-rings in static face seals. Journal of Applied Polymer Science, 135(33), 46582.
Gupta, S., & Roberts, A. (2022). Machining versus molding for PTFE O-rings: Dimensional accuracy and cost trade-offs. Sealing Technology, 2022(5), 7–13.
Hernandez, L., & Kim, D. (2017). Leak rate prediction for PTFE O-rings with non-standard inner diameters. Tribology International, 112, 140–148.
Jones, P. E., & Liu, C. (2020). The effect of groove design on PTFE O-ring extrusion resistance at pressures up to 40 MPa. Journal of Pressure Vessel Technology, 142(6), 061203.
Martin, G., & Zhao, Y. (2019). Large diameter PTFE O-rings made from bonded cord: strength and dimensional repeatability. Polymer Testing, 78, 105942.
Nakamura, T., & Anderson, B. (2021). Material certification and dimensional reporting for PTFE seals in pharmaceutical valves. Pharmaceutical Engineering, 41(3), 62–69.
Owen, M. S., & Li, J. (2018). Tolerance stack-up analysis for PTFE O-ring grooves in high-pressure hydrogen fittings. International Journal of Hydrogen Energy, 43(48), 21709–21718.
Still unsure which PTFE O-ring size fits your groove? Send your groove drawing, fluid type, and operating temperature to Ningbo Kaxite Sealing Materials Co., Ltd. Our engineers will verify your dimensions and recommend a standard or custom size before you commit to a purchase order.
Ningbo Kaxite Sealing Materials Co., Ltd. is a specialized sealing manufacturer that helps global buyers source PTFE O-rings, gaskets, and custom seals in exact sizes and tight tolerances. With in-house tooling, full material traceability, and fast sample service, the company reduces the risk of size mismatch and sealing failure. Visit https://www.kaxiteseal.com or email [email protected] for a same-day size check and quotation.
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