Abstract: To better meet the demand for high-precision and rapid measurement of external thread parameters, an online measurement system based on two linear laser sensors is proposed. Through eye-to-hand calibration to establish the spatial transform matrix between the CCD camera and the robotic arm, the motion of the measurement unit driven by an image-guided robotic arm is achieved. The calibration of the flat plug gauge is realized by controlling the pose of the robotic arm and the real-time feedback from the linear laser sensors’ data. The linear laser sensors collect the thread profile data, fit the major and minor diameter profiles using the least squares method, iteratively determine the pitch diameter line, and calculate the external parameters of major diameter, minor diameter, pitch diameter, and pitch. By analyzing the sources of error in the measurement system, the expanded uncertainty of the pitch diameter measurement is calculated to be U = 6.3 μm. Comparative experimental results indicate that this measurement system can achieve high-precision and high-speed measurement of external thread parameters.