Quick answer. Diameter tolerance limits the size of round wire. Ovality limits the difference between the largest and smallest diameter readings at the same cross section. Check both against the purchase specification. Wire can pass the diameter band and still fail a separately specified ovality limit.
Why both checks matter
A wire feed guide, forming die or precision pin may need a consistent fit as the wire turns. The diameter band controls size. The ovality limit controls how much that size can differ with measuring direction at one point along the wire. Readings taken far apart along a coil show size variation along its length and should be recorded separately.
For example, suppose a buyer calls for 1.000 ± 0.020 mm and a separate 0.010 mm maximum ovality. At one cross section the operator records a smallest reading of 0.989 mm and a largest reading of 1.006 mm.
| Check | Result |
|---|---|
| Diameter band | Both readings are within 0.980–1.020 mm. Pass. |
| Ovality | 1.006 − 0.989 = 0.017 mm. This exceeds 0.010 mm. Fail. |
These limits are for the example. Use the values and measurement method agreed for your order.
How to measure at receiving
- Identify the sample. Match the coil or spool to the purchase order and lot identification. Take the required samples at the agreed locations. Keep the wire in its received condition for measurement.
- Select the instrument. Use a calibrated outside micrometer with suitable resolution and measuring force for the tolerance. Clean the anvils, check zero, and use the instrument’s constant force control where specified.
- Measure across the same section. Align the wire square to the measuring axis. Repeat at the angles prescribed by the inspection plan. If the plan calls for maximum and minimum readings, check enough orientations to locate them. Two arbitrary readings can miss the extremes.
- Record both decisions. At each location, compare the diameter readings with the size limits, then compare the difference between the extremes with the ovality limit. Keep the lot, locations, readings and instrument reference with the result.
For very fine or easily deformed wire, agree on the gauge and force before inspection. If the drawing requires a roundness profile, use its specified measurement method.
What to put on the purchase order
Confirm grade, nominal diameter and limits, finish, condition, supply form and the applicable specification and edition. ASTM A580/A580M is a specification for stainless steel wire, and ASTM A555/A555M covers general requirements for stainless steel wire and wire rods. Confirm which documents govern your order. For a separate ovality requirement, state its limit and the measurement and sampling method. Include any required records with the inquiry.
For a product reference, see 304 stainless steel bright wire. Send the actual size band and ovality requirement so they can be checked against your order.
Post time: Nov-10-2026