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Surface · Metal body panels (steel and aluminum)

Aluminum body panels: measuring paint with an eddy-current gauge

Paint over aluminum needs an eddy-current (NFe) gauge; a steel-only gauge is the wrong tool. Which panels are often aluminum and what to check.

Also listed as aluminum panels, non-ferrous panels, NFe panels

By Watchmarks EditorialUpdated

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Short answer

Paint over aluminum is measured with an eddy-current gauge in NFe mode, DeFelsko says; a steel-only (Fe) gauge is the wrong tool. Recent vehicles can combine steel doors and fenders with aluminum hoods and roofs, so check which mode your gauge is in on each panel. As on steel, the reading is the whole paint stack down to the metal.

Key facts

Material
Aluminum and other non-ferrous metals[1]UNI-T: NFE means non-magnetic metals such as aluminum and copper.
Gauge method
Eddy current[2][3]
Gauge mode
NFe; examples include DeFelsko's N probes and the PosiTest DFT-Combo[4][3]
What the reading includes
Everything between the probe and the metal: primer, base color, clear coat, any repaint, filler and dirt[3]DeFelsko: magnetic and eddy-current gauges make no distinction between layers.
Published thickness figures
No aluminum-specific figure in our sources; DeFelsko's 100-180 µm is typical factory paint overall[3]Not a pass/fail line.
Polishing note
A Fe/NFe reading cannot tell you how much clear coat is left[3]The reading is total coating thickness, not clear-coat thickness. See [clear coat](/surfaces/clear-coat) for DeFelsko's figures.
Inspection tip
Hoods and roofs are common aluminum panels on recent cars; confirm the gauge is in NFe mode there[2]Actual materials vary by vehicle.

Watch out for

  • A Fe-only gauge is the wrong tool. UNI-T's FE mode is for magnetic substrates such as iron and steel; aluminum needs NFe (eddy current).
  • Watch automatic switching. UNI-T specifies automatic or manual substrate identification on the UT343E, and Elcometer's 311 FNF switches automatically. Confirm the mode the gauge picked before trusting the number.
  • Thin aluminum can limit accuracy. Elcometer says the 311's stated accuracy needs at least 300 µm of aluminum under the probe; Linshang lists 0.05 mm minimum non-ferrous substrate for the LS221.

What fits

Product details below are the seller's own description unless a source is shown. Pick the variant named for each item.

  • Fe/NFe combination gauge

    UNI-T UT343E Fe/NFe coating thickness gauge (Bluetooth, 0-2000 µm)

    Choose the UT343E (Bluetooth, 0-2000 µm), the only variant listed.

    UNI-T specifies it for ferrous and non-ferrous substrates with automatic or manual substrate identification. The AliExpress store uses UNI-T's name, but UNI-T's own where-to-buy page links no AliExpress store, so treat the seller as unconfirmed. UNI-T's page lists CE and UKCA marks only.

    Sold by UNI-T Official Store

    View on AliExpress Opens aliexpress.us

Questions

Will a magnetic paint gauge work on aluminum?

No. DeFelsko says paint over aluminum and other non-ferrous metals is measured with eddy-current gauges, and UNI-T's FE mode is for magnetic substrates such as iron and steel. You need NFe capability.[2][1]

Which panels are likely to be aluminum?

DeFelsko notes that recent vehicles can combine steel doors and fenders with aluminum hoods and roofs. Materials vary by car, so a combination gauge that identifies the substrate, or lets you switch to NFe, is the practical answer.[2][5]

Sources

  1. Coating Thickness Gauges FAQ · UNI-TREND Technology (UNI-T) · UNI-T FAQ on what coating thickness gauges measure and what FE/NFE mean. · checked 2026-10-07
  2. Automotive Paint Inspection - Paint Meters · DeFelsko Corporation · DeFelsko article on used-vehicle paint inspection: measurement principles by substrate, inspection method, and a rust-repair case study (PosiTest DFT Combo). · checked 2026-10-07
  3. How to Use Paint Thickness Gauges for Better Automotive Detailing · DeFelsko Corporation · DeFelsko detailing guide: what paint gauges measure, typical factory film builds, F/N display codes, units, PosiTest DFT, PosiTector 6000 and PosiTector 200 options. · checked 2026-10-07
  4. PosiTector 6000 Paint Thickness Gage · DeFelsko Corporation · DeFelsko PosiTector 6000 product page: F/N/FN probe types, probe ranges and accuracy, certificate, warranty, standards, FAQ on calibration and adjustment. · checked 2026-10-07
  5. UT343E Coating Thickness Gauge · UNI-TREND Technology (UNI-T) · UNI-T UT343E product page (global site): range, resolution, accuracy, listed certificates, battery, app, substrate identification. · checked 2026-10-07
  6. Elcometer 311 Automotive Paint Meter · Elcometer · Elcometer 311 automotive paint meter: range, accuracy, resolution, minimum substrate thickness, FNF auto switching, Bluetooth (Model T), warranty. · checked 2026-10-07
  7. LS221 Split-Type Coating Thickness Gauge · Linshang Technology · Linshang LS221 product page: principles, range, accuracy, resolution, curvature and substrate limits, standards, package contents, page markup. · checked 2026-10-07

Next review due 2027-01-07.