The procedures in these test methods may be used for the acceptance testing of commercial shipments, but caution is advised because technicians may fail to get good agreement between results on certain yarns, cords, or fabrics. Comparative tests as directed in Section 5.1.1 may be advisable.

If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, test samples should be used that are as homogeneous as possible, that are drawn from the material from which the disparate test results were obtained, and that are randomly assigned in equal numbers to each laboratory for testing. Other materials with established test values may be used for this purpose. The test results from the two laboratories should be compared using a statistical test for unpaired data, at a probability level chosen prior to the testing series. If a 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.

The significance and use of particular properties are discussed in the appropriate sections of the specific test methods.

1.1 These test methods cover the testing of industrial yarns made of glass filaments, cords twisted from such yarns, and fabric woven from such cords—products that are made specifically for use in the manufacture of pneumatic tires. By agreement, these test methods may be applied to similar glass yarns and cords used for reinforcing other rubber goods and for other industrial applications. The yarn or cord may be wound on cones, tubes, bobbins, spools, or beams, woven into fabric, or in other forms. These test methods include testing procedures only. These test methods do not include specifications or tolerances.

1.2 No procedure is included for the determination of fatigue resistance of cords, but several articles relating to the measurement of fatigue resistance of cords made from man-made filaments and cured in rubber were published in the bibliography of Test Methods D885.