5.1 This test method is not recommended for the acceptance testing of commercial shipments of wool top, card sliver, or scoured wool since the referee method, Test Method D2130, is recommended for that purpose. Although this test method is not recommended for acceptance testing, it is useful for fast quality control checks.

5.1.1 If there are differences of practical significance between reported test results for two laboratories (or more), comparative test should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, use the samples for such a comparative test that are as homogenous as possible, drawn from the same lot of material as the samples that resulted in disparate results during initial testing and randomly assigned in equal numbers to each laboratory. The test results from the laboratories involved should be compared using a statistical test for unpaired data, a probability level chosen prior to the testing series. If bias is found, either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.

5.2 The specific area of the wool fibers is measured by the resistance in air flow. The resistance to air flow has been related to average fiber diameter measured by the microprojection method. The instruments have been calibrated to read average diameter in micrometres. Although the reading is affected by the average fiber diameter distribution of the specimen, the results secured by the instruments give no indication of this distribution. However, in converting the micrometres reading to millitex units (Annex A1), low, medium, and high standard deviations were used in the calculations to arrive at the range of millitex units which accordingly reflect the distribution of fiber diameters.

1.1 This test method covers the estimation of the average fiber diameter of wool fibers by use of the Port-Ar and the WIRA Fiber Fineness Meter instrument, which operate on the air-flow principle. Other air-flow instruments have not been tested with this method. The method is directly applicable to non-medullated, carded wool and wool top.

1.2 This test method is applicable to grease wool and scoured wool after the samples of such materials have been prepared as directed in Test Method D2130.

Note 1: The use of the Micronaire instrument for measuring the fineness of cotton fibers is covered in Test Method D1448.
 The assignment of grade for wool and mohair is covered in Specifications D3991 and D3992.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.