REFERENCE

Tubing glossary: terms used on data sheets and in our guides

Plain-language definitions of the terms used on tubing data sheets, in our product tables and in our guides. Values on our data sheets are stated at 23 °C unless noted. For a quick unit conversion, use the tubing unit converter.

Dimensions and tolerances

Outer diameter (OD): The measurement across the outside of the tube. The OD is the dimension that has to match a push-in fitting. See matching tubing to fittings.
Inner diameter (ID): The measurement across the bore of the tube. The ID sets the flow area and, together with the OD, the wall thickness.
Wall thickness: Half the difference between OD and ID: (OD − ID) ÷ 2. At the same OD, a thicker wall carries more pressure. See high-pressure plastic tubing.
Tolerance: The allowed variation from the stated dimension. Our nylon tubing tables list a tolerance of ±0.10 mm.
Nominal size: The size a product is called by, such as 1/4 in, which can differ slightly from the measured dimension. Check the actual OD and ID in the table.
Metric and inch (fractional) sizes: Two separate size systems. A 6 mm tube and a 1/4 in (6.35 mm) tube are not the same OD and do not fit the same fitting. See the tubing size chart.
Roll length: The length of tubing supplied on one coil or spool. Standard roll lengths are listed on each product page.

Pressure and temperature

Working pressure: The pressure a tube is rated to carry in service at the stated temperature. Design to the working pressure, not the burst pressure. See the pressure and temperature guide.
Burst pressure: The pressure at which a tube fails in a test. It shows the margin above the working pressure and is not a rating to operate at.
Bar: A metric unit of pressure used on our tables. One bar is 100 kPa, or 0.1 MPa.
psi: Pounds per square inch, the common US unit of pressure. Convert with the unit converter.
kgf/cm²: Kilogram-force per square centimeter, an older metric unit still found on some data sheets. It is close to one bar.
Derating: Lowering the allowed working pressure as the temperature rises. The factors are in the pressure and temperature guide.
Temperature range: The lowest and highest temperatures a tube is rated for. The range on a data sheet and the pressure rating are linked, so read them together.
Bend radius: The tightest curve a tube can follow without kinking, measured to the tube center. A smaller bend radius means a more flexible tube. See the bend radius guide.
Kink: A sharp fold that collapses the bore when a tube is bent tighter than its bend radius. A kink restricts flow and can damage the tube.

Materials

PA6 (nylon 6): Polyamide 6. A firm, strong nylon with the highest working pressures in our nylon range. See PA6 nylon tubing.
PA12 (nylon 12): Polyamide 12. Generally more flexible than PA6, used where routing and flexing matter. See PA12 nylon tubing and the PA6 vs PA12 comparison.
Polyurethane (PU): A flexible, resilient tubing material used for compressed air. Our PU tubing data sheet gives a hardness of 98 ± 2 Shore A.
Polyether TPU: Thermoplastic polyurethane made with a polyether base. It resists hydrolysis (breakdown by water) better than polyester-based PU. See polyether vs polyurethane tubing.
Hydrolysis: Chemical breakdown of a material by water, faster in heat and humidity. It is the main reason to choose polyether over polyester-based polyurethane in damp conditions.
FEP: Fluorinated ethylene propylene, a fluoropolymer used where broad chemical resistance is needed. See FEP tubing.
PFA: Perfluoroalkoxy alkane, a fluoropolymer related to FEP. See PFA tubing and FEP vs PFA.
PE (polyethylene): A lightweight plastic used for air and water lines. See PE tubing and the PE tubing guide.
Shore hardness: A scale for how hard a plastic or rubber is. Shore A is used for soft materials such as polyurethane, Shore D for harder ones such as nylon; a higher number is harder within a scale. See tubing Shore hardness for the values on our data sheets.
Chemical resistance: How well a material withstands contact with a given chemical at a given temperature and concentration. Ratings describe a material family, not one grade. See the chemical resistant tubing guide.

Construction and fittings

Pipe, tube, tubing and hose: In compressed-air work, “PU pipe” and “pneumatic pipe” are common names for flexible plastic tubing sold on a roll, the same product as the tubing on a data sheet. “Pipe” can also mean rigid steel or PVC pipe, and “hose” usually means a heavier or reinforced flexible line. State the material, OD and ID when you order. See PU pipe and pneumatic pipe vs tubing.
Composite (two-layer) tubing: Tubing with an outer layer of one material over an inner layer of another. Our composite tubing comes as V8 (PU outer, PA12 inner) and V9 (polyether TPU outer, PA12 inner).
Recoil (coiled) tubing: Tubing formed into a spiral so it stretches in use and returns to its coiled shape. See PU recoil tubing.
Flame-retardant tubing: Tubing made with a formulation that resists ignition and burning. Check which standard it was tested to before you rely on it.
Antistatic (static-dissipative) tubing: Tubing made to let static charge drain away instead of building up. The ESD Association separates conductive (below 1 × 10⁴ ohms), static dissipative (1 × 10⁴ to 1 × 10¹¹ ohms) and insulative materials, so state the resistance range and test method. See antistatic PU tubing, made to order.
Multi-lumen (multi-bore, multi-core) tubing: Tubing with two or more channels in one piece, joined along their length. It is not the same as a tube bundle, which carries separate tubes in a shared jacket. See multi-lumen tubing, made to order.
Push-in fitting: A connector that grips the tube OD when the tube is pushed in. The tube OD and wall must suit the fitting. See matching tubing to fittings.
Pneumatic tubing: Plastic tubing for compressed-air lines, usually PU, nylon or PE. See the pneumatic tubing guide.

Documents and ordering

Technical data sheet: The document that lists a tubing family’s dimensions, pressure, temperature and physical properties. Download ours on the data sheets page.
Test report: A document that records the result of a specific test on a specific batch or sample. See how to read certificates and test reports.
Batch (lot): A group of tubing made in one production run. A test result applies to the batch it was measured on.
MOQ (minimum order quantity): The smallest quantity we supply per specification. Our standard terms are on the wholesale page.
OEM and custom tubing: Tubing made to your own OD, ID, color, length or material. See OEM and custom tubing.

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