FED-STD-228A
Method 1221.1
18 April 2014
THICKNESS, WOVEN OR BRAIDED METAL ARMOR;
MICROMETER CALIPER
1. SCOPE
1.1 This method is intended for use in determining the thickness of woven or braided metal armor. It is
recommended for use when the wire or cable has an over-all diameter of less than one inch.
2. SPECIMEN
2.1 The specimen should be a piece of the inspection unit at least 2 feet in length.
3. APPARATUS AND REAGENTS
3.1 The apparatus and reagents shall be as follows:
3.1.1 Micrometer caliper graduated to read in mils or 0.0001 inch and having flat surfaces on both anvil
and end of spindle each approximately 0.25 inch in diameter. The surfaces of the spindle and anvil shall
be parallel to within 0.0001 inch.
3.1.2 Wiping cloth.
3.1.3 Alcohol or other suitable solvent.
4. PROCEDURE
4.1 The specimen shall be free from mechanical damage. Any dirt, grease, or other extraneous
materials shall be removed from the specimen by means of the cloth and solvent. The micrometer caliper
shall be applied directly over the armor so that the anvil and spindle are just brought into contact with the
specimen in such a manner that the armor is not distorted. The criterion of contact is the initial
development of frictional resistance to the movement of the specimen between the micrometer surfaces.
The diameter over the armor shall be read from the micrometer scale and the value recorded as D1.
4.2 The armor shall be removed from the specimen and the diameter over the core (assembly under the
armor) determined and the value recorded as D2. The micrometer caliper shall be applied directly over
the core so that the specimen can just be moved between the anvil and spindle without distortion of the
core.
4.3 Three measurements equally spaced along the length of the specimen shall be made. The diameter
over the armor and over the core shall be determined as nearly as practicable at the same point.
5. RESULTS
5.1 Calculation. The thickness of the armor at any point shall be calculated as follows:
Thickness, inch=D1-D2
2
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