Reference
Glossary of Roundness & Die Measurement Terms
Plain definitions of the geometry, tooling and metrology terms used across wire drawing, tube and metal-forming quality control.
Geometry & form
Ovality
The degree to which a nominally circular cross-section has become elliptical, normally expressed as (Dmax − Dmin) as a percentage of nominal diameter. See the ovality calculator.
Out-of-roundness
The absolute difference between the largest and smallest diameter of a cross-section, in millimetres, inches or microns. Some standards express it as a radial value equal to half that range.
Circularity
A broader form tolerance describing how closely a profile matches a perfect circle, capturing three-lobe, multi-lobe and irregular deviation that a two-point ovality figure cannot detect.
Lobing
Periodic deviation from roundness with a repeating number of lobes. Two-lobe form is ovality; three or more lobes usually indicate chatter, clamping distortion or a centreless grinding artefact.
Concentricity
How well the centre of one circular feature aligns with the centre of another — for example a die bore relative to the die case.
Runout
Total variation observed at a fixed point while a part is rotated through one revolution. Combines roundness error and eccentricity.
Best-fit circle
The circle that minimises deviation across all measured contour points. Its radius gives an unbiased mean diameter, and the residuals give circularity.
Best-fit ellipse
An ellipse fitted to the measured contour. Its major and minor axes give ovality directly, and its orientation shows where on the part the deviation lies.
Wire drawing & tooling
Drawing die
The tool through which wire, bar or tube is pulled to reduce its cross-section. Its bore geometry is transferred directly to the product.
Nib
The hard insert — typically tungsten carbide, natural diamond or polycrystalline diamond — forming the working bore, held in a steel case.
Bearing
The short parallel land in the die bore that sets the final diameter. Wear here is the primary driver of both size drift and ovality.
Approach angle
The conical entry region where material deformation occurs. Affects drawing force, lubrication and wear distribution.
Reduction ratio
The proportional decrease in cross-sectional area through a single die pass.
Die reconditioning
Re-polishing a worn bore back to a usable geometry. Frequently restores diameter without restoring roundness, which is why measured verification matters.
Capstan
The driven drum that pulls wire through the die and controls tension between passes.
Measurement
Sub-pixel edge detection
Locating a feature boundary to finer than one pixel by interpolating the intensity gradient across the edge transition. Lifts optical accuracy beyond the raw sensor resolution.
Microns per pixel
The calibration scale relating image pixels to physical distance. Without it, an image yields only relative geometry.
Measurement uncertainty
The quantified doubt about a result. A measurement reported without uncertainty is an opinion.
Confidence score
MeasureMaster's combined indicator of edge quality, contour continuity and fit residual, showing how much the system trusts its own reading.
Non-contact measurement
Measuring without touching the part, avoiding measuring-force error and surface damage on soft or polished components.
Traceability
An unbroken chain of calibrations linking a measurement to a national or international standard.
Condition-based monitoring
Servicing tooling according to its measured state rather than a fixed calendar — the practical goal of measuring die ovality routinely.
Put the terms to work
Measure ovality, circularity and confidence on a real part in your browser.