Internal thread is detected by thread plug gauge, and external thread is detected by thread ring gauge. The thread detection device is a standard plug gauge that meets the requirements of the drawings. M4 nutlets must be produced in large quantities, and it is unrealistic to detect each one. Therefore, the most effective method is to grasp the link of production quality and urge manufacturers to use standard wear-resistant threaded nuts. For example, YAMAWA tap is made of powder high-speed steel containing 5% cobalt, which has good toughness and high hardness, so it is wear-resistant. This is mainly due to the addition of cobalt. In the production process, thread tapping is tested after a certain amount of tapping. The test method uses the same standard ring gauge to tap the old thread. If it is loose, it will be worn out. If it is worn out, replace it immediately. The quality of nut depends on the precision of tapping, so that tapping can achieve high qualified rate.