This study was carried out to determine some test variables on Zwick 1511 yarn strength tester. To determine the suitable number of breaks for any sample, the suitable test speed for different yam counts for the standard time to break (20±3Sc.) and the effect of pre-feeding actual or nominal yam count on yam strength values. Giza 88 Egyptian Extra-Long Staple cotton variety was used to spin six combed yam counts; 30s. 40s. 60s. 80s, 100s, and 1205, at twist constant of (3.6). It was found that the test sample size of 40 breaks is more acceptable and optimum from the stand-point of degree of precision and also saving testing time. It was found that speed (70) is acceptable speed for fine counts (60s - 120s) and speeds (80-90) for medium counts (30s-40s). Considering the differences between the ac­tual and nominal yam counts to input information to Zwick 1511 single yarn strength tester, it was found important to input the actual yarn count.