1. Choose the wrong sewing thread, if the material or sewing requirements are not clear, the bottom thread is not properly matched;
2. The quality of the sewing thread itself has defects, such as fluffing, insufficient strength, loose stock, lack of stock, etc.;
3. The needle number is useless, which causes the needle and thread size to not match;
4. The needle or needle hole of the sewing machine is damaged or defective;
5. The tension of the sewing thread is too large, and the tension of the sewing thread channel of the machine is not adjusted properly;
6. Incorrect threading or improper sewing machine operation;
7. The needle eye is hot, and the sewing thread does not have enough lubrication, that is, the oiling rate is not enough.
8. The feeding process is not smooth or the feeding method is inappropriate.