Low MU Permeability Indicator

The Low Mu Permeability Indicator is a simple, rugged, non-destructive inspection instrument developed for laboratory, shop and field use. The GO, NO-GO feature permits instant acceptance testing of austenitic stainless and Manganese steel base and weld materials. The Indicator requires no external standards, no adjustments, no visual readings and is unaffected by position. It performs equally well on sheets, plates, rods, irregular shaped objects and individual parts of complex components. It is effective in locating areas of high or low permeability in heterogeneous products and has application where cold forming and annealing operations are required.



The Indicator weighs 3 oz. and is 5 inches long making it comfortable for hand held operations. All metal components are bright Nickel plated. The Indicator and it’s Inserts are furnished in a customized case. The Indicator conforms to SEV-ENG-96001, the replacement specification for MIL-I-17214B.


The operation of the Indicator is based on the mutual attraction of a permanent bar magnet to a known standard and an unknown material. In use, an Insert is screwed into the top of the case. The magnet is then attracted to the Insert by a force dependent upon the Insert’s designated permeability. The end of the magnet projecting from the opening in the bottom of the case is then brought in contact with the material being tested. The Indicator is moved away in a direction perpendicular to the contact surface. If the material being tested has a permeability higher than that of the insert, the magnet will first break contact with the Insert as the Indicator is moved away. On the other hand, if the permeability of the material being tested is lower than that of the Insert, the magnet will first break contact with the material as the Indicator is moved away. Thus, by interchanging inserts, it is possible to bracket the permeability of the material being tested.

Available Insert Values

The Indicator is available with any combination of Inserts. Available Insert values are:

1.01 Mu 1.02 Mu 1.03 Mu 1.04 Mu
1.05 Mu 1.06 Mu 1.08 Mu 1.09 Mu
1.10 Mu 1.15 Mu 1.20 Mu 1.30 Mu
1.40 Mu 1.50 Mu 1.60 Mu 1.80 Mu
1.90 Mu 2.00 Mu 2.20 Mu 2.50 Mu
3.00 Mu 3.50 Mu 4.00 Mu 4.50 Mu
5.00 Mu 5.50 Mu 6.00 Mu  

Four Inserts are included in the price of each Indicator. There is a charge for each additional Insert. All Inserts are calibrated for a specific Indicator. When ordering, please specify the Inserts desired. Instruments are delivered fully calibrated with a certificate of calibration showing the required values and quality information for the Instrument. Permeability Indicators need to be recalibrated annually.


Instructions for Use