A hose purchase order should state acceptable dimensional ranges, not only nominal sizes. Inside diameter, outside diameter, wall thickness and length influence fitting compatibility, pressure performance, weight and the buyer’s ability to sell a consistent product.
Nominal size is a product name. Tolerance defines what can actually be accepted.
Distinguish ID, OD and Wall Thickness
Inside diameter controls flow and fitting insertion. Outside diameter affects clamps, sleeves and routing space. Wall thickness contributes to construction but should not be used alone to infer pressure capability.
For many hoses, the relationship is approximately:
OD = ID + 2 × wall thickness
Reinforced and corrugated constructions may require a product-specific measurement method. Define where and how the measurement is taken.
Write Limits, Not Vague Terms
“Approximately 25 mm” is difficult to inspect. A controlled specification provides a minimum and maximum or a nominal value with a plus/minus tolerance.
| Weak requirement | Controlled requirement |
|---|---|
| 1-inch hose | ID range stated in mm |
| Standard wall | Nominal wall and tolerance |
| 100-meter roll | Length tolerance and measurement method |
| Fits camlock | Hose tail OD and clamp method identified |
The acceptable range should reflect the product standard, manufacturing process and application. Do not copy a tolerance from an unrelated hose construction.
Link Dimensions to Fittings
Hose and fitting specifications should be reviewed together. A hose may meet its own ID tolerance yet provide poor retention if the hose-tail geometry, clamp range or assembly method is unsuitable.
For an assembly, define:
- Hose ID and OD range
- Fitting material and hose-tail dimensions
- Clamp type and range
- Insertion depth
- Assembly orientation
- Required pressure or pull-off test
This is particularly important when components come from different suppliers.
Control Length and Coil Quantity
State whether length is measured under tension, relaxed or at a defined condition. For cut assemblies, identify whether fitting length is included.
For coils, agree whether the quantity is controlled by measured length, weight conversion or both. If weight is used as a production check, the approved weight-per-meter range must be established.
Build an Inspection Table
The purchase order or attached specification should list each characteristic, nominal value, tolerance, method and sampling requirement. This gives purchasing, supplier QC and receiving inspection one shared reference.
Do not resolve dimensional disagreement using website text or an old quotation. The current approved drawing and PO revision should control the order.
Buyers can review published ID, OD and pressure combinations for clear reinforced PVC hose and PVC steel wire hose. Contact Sunhose to confirm a production tolerance before ordering.
Frequently Asked Questions
Why can two hoses with the same nominal size fit differently?
Nominal size may not describe the complete dimensional range. Construction, ID tolerance, OD and hose-tail design all influence fit.
Should wall thickness be calculated from ID and OD?
It can be used as a cross-check for uniform constructions, but direct measurement and the specified method should control acceptance.