Yarn has sufficient tensile strength to withstand the stresses of preparation and fabric manufacture. The main function of twist is to give coherence to the yarn i.e. twist provide strength to the yarn. The cohesion arises mainly from the twist, which presses the fibres together, as the stretching forces are applied & thus, developing friction between adjacent fibres. The equipment used for determination of twists of a yarn is known as a Twist Tester.