Abstract: Thread joint is one of the most widely used joint in industry,agriculture and daily life.The quality of thread is an important element which determining its reliability.Some high demanding fasteners must be detected one by one.Detection process is a series of repeated actions.Specially designed automation equipment can greatly reduce the labor intensity,enhance the efficiency of detection.Therefore,the control system for automatic internal thread detection machine has been developed.This system aimed to realize the automatic detection of a certain size range of internal thread and digital detection results.PLC as the core control component,has realized the coordinated control of parts of the control system.Using the touch screen as human-computer interaction,can realize real-time display system status and test results.

Key words: thread joint, PLC, automation, touch screen