This series of automatic thread trimmers is composed of cutter head, lower thread trimmer drive part, thread release part, presser foot lifter, ST or WP and other parts. The electromagnet model of the presser foot lifter is DS-7598, the voltage is 24V-32V, and the resistance is 3.5Ω±10. The electromagnet model of the lower trimming drive part is DS-7465, the voltage is 24V-32V, and the resistance is 3.5Ω±10. The rotating electromagnet model of ST or WP configuration is DS-342, voltage 24V-30V, resistance 13Ω±10.