The effect of cutting fluid on the operation of a thread tapping process is investigated. Several sets of orthogonal array experiments were designed and conducted on steel workpieces to determine the relationship between cutting fluid properties and the resulting threadform quality. Variables examined in the experiments included tapping speed and cutting fluid type. Response variables chosen were the pitch and functional diameters of the threads. The results of the experiments show that the properties of the cutting fluid have a statistically significant effect on the size and quality of the threaded hole.