Surface · Metal body panels (steel and aluminum)
Steel body panels: measuring paint with a magnetic (Fe) gauge
Paint over steel is read in Fe (magnetic) mode. What the number includes, why filler can fool some gauges and why NFe still helps on steel.
Also listed as steel panels, ferrous panels, Fe panels
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Short answer
Paint over steel is measured with a magnetic gauge in Fe mode. The reading is the whole stack down to the steel, including any repaint or filler. DeFelsko warns that steel particles in body filler can fool some magnetic instruments, and AUTO BILD notes that tin-filled repairs on a steel body show up only on a gauge that also has NFe capability, so a combination gauge is the safer choice for steel cars too.
Key facts
- Material
- Steel (ferrous metal)[1]
- What the reading includes
- Everything between the probe and the metal: primer, base color, clear coat, any repaint, filler and dirt[3]DeFelsko also warns that steel particles added to body filler can fool some magnetic instruments.
- Published thickness figures
- DeFelsko: factory paint typically 100-180 µm; about 75 µm on some roofs and about 430 µm on some SUV rocker panels[3]DeFelsko says there is no absolute right thickness. 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
- Check steel panels in NFe mode too: AUTO BILD says tin-filled repairs on steel need NFe capability to find[5]
Watch out for
- Filler can fool some magnetic gauges. DeFelsko warns that, even on steel, some magnetic instruments can be fooled when steel particles are added to body filler.
- Tin needs NFe. AUTO BILD notes that tin-filled repairs on a steel body can only be found with a gauge that also has NFe (eddy-current) capability. See tin-filled repairs.
- Zero on bare steel first. DeFelsko tells users to check a gauge on an uncoated part, then on the shims laid on the bare surface, and says cheaper instruments drift and should be checked before use each day.
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
Is a steel-only (Fe) gauge enough for a used car?
It reads paint on steel panels, but AUTO BILD notes that tin-filled repairs on a steel body show up only on a gauge with NFe capability, and DeFelsko notes that many recent cars also have aluminum hoods and roofs. A combination Fe/NFe gauge covers both.[5][2]
Can body filler fool a magnetic paint gauge?
Sometimes. DeFelsko warns that some magnetic instruments can be fooled when steel particles are added to body filler. It also says a gauge giving no reading may be beyond its limit, which could mean filler.[2]
How do I check my gauge before measuring steel panels?
DeFelsko suggests a zero check on an uncoated part, then a reading on the included plastic shims laid on the bare surface. It says separately sold coating thickness standards are more accurate than shims.[3]