--- title: "Push-In Fittings and Tubing: How to Match Tube OD, Tolerance and Material" canonical: "https://yuannaitube.com/push-in-fittings-tubing-match/" language: "en-US" --- RESOURCES # Push-In Fittings and Tubing: How to Match Tube OD, Tolerance and Material By [YUANNAI TUBE]() Published 2026-10-26Updated 2026-11-05 ![Blue, black and clear tubing seated in push-in fittings with cut samples and a caliper]() A push-in fitting grips the **outside diameter** of the tube, so the match starts with OD, then tolerance and tube material. This guide covers pneumatic and industrial push-in (push-to-connect) fittings, not plumbing push-fit fittings for water pipes. It shows which tube OD goes with which fitting size, why metric and inch sizes do not swap, and what to check at installation. **Quick answer.** Choose the tube OD the fitting is marked for, in the same system (metric or inch). Keep the OD inside the fitting maker’s tolerance, cut the tube square, insert it fully to the stop, and check that the fitting’s pressure and temperature rating covers the line. The lower rating of tube and fitting governs. ## Match on OD, not ID The collet and seal inside a push-in fitting work on the outer surface of the tube. ID sets flow, and **wall thickness** (OD minus ID, divided by two) affects pressure and bend, but the fit dimension is the OD. In every model table on this site the OD is listed beside the ID, so you can read both from one row; see [tubing ID, OD and wall thickness]() for how they relate. ## Metric and inch sizes do not swap Metric and inch tubes look alike, but their ODs differ by more than the tolerance listed for each model (±0.10 mm). These pairs come from the model tables: | Metric OD (mm) | Nearest inch size | Inch OD (mm) | Difference (mm) | | --- | --- | --- | --- | | 6.0 | 1/4″ | 6.35 | 0.35 | | 10.0 | 3/8″ | 9.525 | 0.475 | | 12.0 | 1/2″ | 12.70 | 0.70 | The 4, 8, 14 and 16 mm sizes have no inch size close enough to compare. Pick the tube in the same system as the fitting, and write that system into your [tubing specification]() . ## One OD, several walls An 8 mm OD tube comes with different IDs, and all of them go into an 8 mm fitting. The wall changes pressure and flow, not the fit. From the PA12 table: | Model | ID (mm) | OD (mm) | Wall (mm) | Working pressure at 23°C | | --- | --- | --- | --- | --- | | [YN-PA12 0850]() | 5.0 | 8.0 | 1.5 | 29 bar (426 psi) | | [YN-PA12 0855]() | 5.5 | 8.0 | 1.25 | 19 bar (266 psi) | | [YN-PA12 0860]() | 6.0 | 8.0 | 1.0 | 17 bar (256 psi) | Choose the wall for the pressure and flow the line needs, then confirm the fitting is rated for it. ## Check these at installation - **Cut square** with a tube cutter; an angled or crushed end prevents the seal from seating. - **Insert fully** to the stop, then pull gently to confirm the collet holds. - **Roundness**: a flattened or kinked section near the end will not seal; trim it off. - **Material stiffness**: some fitting makers specify a tube insert or support sleeve for soft or thin-wall tubing. Read the fitting’s tube requirements before choosing PU or PE for a given fitting series. - **Pressure and temperature**: compare the fitting rating with the tube’s **working pressure** at the **operating temperature**, using [working pressure and temperature]() . - **Bend near the fitting**: keep the first stretch of tube straight, and use at least the model’s **bend radius**, such as 35 mm for YN-PA6 0640, so the tube is not levered against the collet. ## If a push-in connection leaks or the tube pulls out Most leaks and pull-outs at a push-in fitting trace back to how the tube end was prepared and seated. The checks below follow the installation and maintenance cautions in the [SMC KQ2 one-touch fitting catalog]() ; read the manual for your own fitting series, because steps differ between makers. 1. **Re-cut the end.** Cut the tube perpendicularly with a tube cutter. SMC warns against pliers, nippers or scissors, which deform the tube and cause trouble. 2. **Re-seat the tube.** Push it slowly and straight into the fitting until it stops, then pull back gently to confirm a positive seal. SMC states that insufficient insertion may cause air to leak or the tube to release. 3. **Trim a reused end.** Polyurethane tube swells under internal pressure, so a used tube may not go back in. Before reusing it, remove the portion that was lodged in the fitting; SMC notes that leaving it on may cause leakage and make removal difficult. 4. **Do not press the release button while inserting.** Pressing it before or during mounting may cause the tube to detach. 5. **Replace, do not mend.** SMC lists cracks, gouges and wear, air leakage, twisted or crushed tube, and hardening, deterioration or softening of the tube as reasons to replace the tube or fitting rather than repair and reuse it. If a fresh, square-cut tube still leaks or pulls out, check the tube OD tolerance against the fitting maker’s requirement. Each model table on the product pages lists the tolerance for this check. To compare a replacement before a bulk order, use the [sample testing guide]() . ## Which material for which fitting use Any of the families on this site can be cut to the same OD, so the fitting does not choose the material; the line does. Moving lines favor [PU]() , fixed pressure lines favor [PA6]() or [PA12]() , and chemical lines use [FEP]() or [PFA]() . The [materials guide]() compares them, and the [pneumatic tubing guide]() covers the whole line. ## Frequently Asked Questions: Tubing and Push-In Fittings What tube goes in a 6 mm push-in fitting? A tube with a 6.0 mm OD, such as the 4.0 × 6.0 mm models (YN-PU 0640, YN-PA6 0640, YN-PA12 0640). A 1/4″ tube has a 6.35 mm OD and belongs in a 1/4″ fitting. Can I use 1/4″ tube in a 6 mm fitting? Use the size the fitting is marked for. The two ODs differ by 0.35 mm, more than the ±0.10 mm tolerance of the model, so they do not swap. Does a thicker wall change the fitting I need? No. The fitting follows the OD. A thicker wall raises the pressure rating and the **bend radius**; confirm the fitting rating covers the line. Do you list fittings? This site lists tubing models. Choose fittings from your fitting supplier’s tube-size chart, and include the fitting’s tube specification in your [inquiry]() so the tube model is matched to it. **Next step.** Find the OD in the [tubing size chart]() , then send the model, fitting series and operating conditions through the [contact form]() . **Related guides:** [pneumatic tubing 6/4 and 8/6 mm]() · [tubing size chart]() · [how to cut plastic tubing]() · [why air tubing kinks]() . ## Sources and scope - [PU Tubing — English data sheet (v3-20261020)]() - [PA6 Nylon Tubing — English data sheet (v4-20261020)]() - [PA12 Nylon Tubing — English data sheet (v5-20261020)]() - [Polyether Tubing — English data sheet (v2-20261020)]() Use these documents for the identified product models and stated test conditions. General material comparisons and selection checklists do not establish a different grade’s rating, fitting compatibility or project approval. 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