Abstract: Optical fiber proof testing equipment has a rotary drive and two pulleys directly coupled to the drive. A fiber is taken from fiber drawing equipment around part of the circumference of the first pulley, along a guide track and around part of the circumference of the second pulley. Respective continuous belts apply a resilient bias to clamp the fiber to the pulleys, the resilient bias being adjustable. The second pulley is marginally greater in diameter than the first pulley so as to establish a predetermined tensile stress in fiber moving between the two pulleys. The test equipment is used after fiber has been drawn in a drawing tower and then coated and before the fiber is stored on reels. The tensile force on the fiber can be changed by changing the diameter of the first or second pulleys. In addition some incremental change in the tensile force can be obtained by adjusting the resilient bias provided by the continuous belt.