---
title: "Rockwell, Brinell, Vickers or Microhardness: Choosing the Right Test | TEK Precision"
url: https://tekprecision.com/blog/hardness-testing-methods-aerospace-parts
description: "A hardness number only means something alongside the method that produced it. How the four main ASTM hardness tests differ, and when aerospace drawings call for each."
lang: en
---

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Quality

# Rockwell, Brinell, Vickers or Microhardness: Choosing the Right Test

TEK Precision September 30, 2026 5 min read

A hardness number only means something alongside the method that produced it. How the four main ASTM hardness tests differ, and when aerospace drawings call for each.

Hardness is one of the fastest ways to confirm that a material has been heat treated correctly, and one of the most common acceptance checks on aerospace drawings. But a hardness value only means something alongside the method that produced it. The indenter, the test force and the way the result is read all differ between methods, and a number on one scale cannot simply be swapped for another.

These are the four test methods most often cited on aerospace drawings and specifications, and what each one is suited to.

## Rockwell (ASTM E18)

The Rockwell test presses a diamond or ball indenter into the surface under a preliminary force, applies an additional force, then removes it and measures the permanent increase in depth. The result is read directly from the tester with no optical measurement, which makes Rockwell fast and well suited to production checks.

Regular Rockwell scales, such as HRC for hardened steels and HRB for softer alloys, use total test forces of 60, 100 or 150 kgf. Superficial Rockwell scales, such as 15N and 30N, use lighter total forces of 15, 30 or 45 kgf with a smaller preliminary force.

## When superficial Rockwell is the right choice

- Thin sections, where a regular test would be influenced by the material underneath
- Case-hardened or surface-treated parts, where the condition of the surface layer is what matters
- Small parts and finished surfaces, where a smaller indentation is preferred

ASTM E18 sets minimum thickness requirements for each scale. If a part is too thin for the scale on the drawing, raise it before testing rather than after.

## Brinell (ASTM E10)

Brinell testing uses a hard ball, commonly 10 mm in diameter, under a high test force, and the diameter of the resulting indentation is measured. The large indentation averages hardness over a broad area, which is why Brinell is typically used on forgings, castings and coarse-grained materials. The same large indentation makes it unsuitable for many finished precision surfaces.

## Vickers and Knoop (ASTM E92)

Vickers testing uses a square-based diamond pyramid, and the diagonals of the indentation are measured optically. Because the indenter shape is the same at every test force, Vickers values are comparable across a wide range of forces and apply to almost any metal, from soft alloys to hardened steel. ASTM E92 also covers the Knoop test, which uses an elongated diamond that produces a shallow indentation suited to thin layers.

## Microindentation hardness (ASTM E384)

At the lowest test forces, Vickers and Knoop testing becomes microindentation hardness testing, covered by ASTM E384. The indentations are small enough to test individual features, thin coatings, case depth profiles and metallographic cross sections.

Microhardness traverses are also used when investigating grinding damage, because abusive grinding can soften or re-harden a thin surface layer. See Grind Burn: The Defect You Cannot See (https://tekprecision.com/blog/grind-burn-detection-nital-etch-inspection).

## Hardness conversions are approximations

Conversion tables such as ASTM E140 relate one hardness scale to another, but the conversions are approximate and depend on the material. When a drawing specifies a scale, test on that scale. Use conversions for reference, not for acceptance, unless the specification explicitly allows it.

## Good practice on any method

- Prepare the test surface as the standard requires. Scale, plating and decarburization all affect results.
- Keep indentations clear of edges and of each other by the distances the standard specifies.
- Verify the tester with certified test blocks close to the expected hardness before testing.
- Test where the drawing or specification requires, not where it is most convenient.

## Hardness testing at TEK Precision

Hardness inspection is performed in TEK's in-house inspection lab (https://tekprecision.com/quality#inspection-lab) to ASTM E-10, E-18, E-92 and E-384. The lab's Wilson hardness testers include superficial capability, and all metrology equipment is calibrated to NIST-traceable standards.

**Related capabilities:** Inspection and test equipment (https://tekprecision.com/quality#inspection-lab) · Special processes (https://tekprecision.com/facilities#special-processes) · Machining capabilities (https://tekprecision.com/products#machining-capabilities)

_Discuss your inspection requirements: https://tekprecision.com/contact._

TP

Written by

TEK Precision

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