DeFelsko PosiTest® FM/GM Coating Thickness Gage


PosiTest FM

The PosiTest® FM/GM Coating Thickness Gage is a magnetic pull-off thickness gage for the Non-destructive measurement of non-magnetic coatings (paint, enamel, plastic, galvanizing, metalizing, plating, etc.) on STEEL.

Magnetic Pull-off

Magnetic pull-off gages use a permanent magnet, a calibrated spring, and a graduated scale. The attraction between the magnet and magnetic steel pulls the two together. As the coating thickness separating the two increases, it becomes easier to pull the magnet away. Coating thickness is determined by measuring this pull-off force. Thinner coatings will have stronger magnetic attraction while thicker films will have comparatively less magnetic attraction. Testing with magnetic gages is sensitive to surface roughness, curvature, substrate thickness, and the make up of the metal alloy.

Magnetic pull-off gages are rugged, simple, inexpensive, portable, and usually do not require any calibration adjustment. They are a good, low-cost alternative in situations where quality goals require only a few readings during production.

Pull-off gages are typically pencil-type or rollback dial models. Pencil-type models (PosiPen shown in Fig 1) use a magnet that is mounted to a helical spring that works perpendicularly to the coated surface. Most pencil-type pull-off gages have large magnets and are designed to work in only one or two positions, which partially compensate for gravity. A more accurate version is available, which has a tiny, precise magnet to measure on small, hot, or hard-to-reach surfaces. A triple indicator ensures accurate measurements when the gage is pointed down, up, or horizontally with a tolerance of ± 10%.

Positest FM/GM

Fig. 1 Pencil-type magnetic pull-off thickness gauge.

Rollback dial models (PosiTest174; shown in Fig 2) are the most common form of magnetic pull-off gage. A magnet is attached to one end of a pivoting balanced arm and connected to a calibrated hairspring. By rotating the dial with a finger, the spring increases the force on the magnet and pulls it from the surface. These gages are easy to use and have a balanced arm that allows them to work in any position, independent of gravity. They are safe in explosive environments and are commonly used by painting contractors and small powder coating operations. Typical tolerance is ± 5%.

Positest FM/GM

Fig. 2. Roll-back dial magnetic pull-off thickness gauge.


  • Highly wear resistant Carbide Probe for longest life and continuous accuracy
  • Modern and up-to-date gauge Scale Ranges fit all applications
  • Conforms to national and international standards including ISO and ASTM.


  • Extra rugged gauge housing, not affected by mechanical shock, water, acid or solvents
  • Unique overall gage design, fully supported, positive positioning, no pivoting tendencies during measurement
  • Gage can be used fully supported or with only the front probe area contacting the surface
  • Functions on a permanent rare-earth cobalt magnet, no battery
  • Explosion Proof – Refinery safe
  • 2 year warranty

Easy to Use

  • Positive visual and audible indicators to designate when thickness reading is established
  • “V” grooves in probe housing and Gauge base allow correct positioning on cylindrical objects
  • Compact, lightweight, precisely balanced, Independent of gravity – Gauge can be used in any position
  • GO/NO-GO button can be pre-set for rapid measurement
  • Probe contact and dial rotation all in a one-finger operation
  • Gauge is furnished with wrist strap and instructions in a high quality leather case with belt loops for your convenience

Positest FM/GM


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