threefold

A threefold cord is not quickly broken.

三股拧成的绳子不易断。

The purpose of the bulkhead is threefold: to seal the forward end of the motor, to retain the pyrogen igniter, and to act as a blowout plug in case of motor overpressurization (discussed earlier).

的目的，舱壁是三个方面：密封着年底汽车，保留热原点火器，并充当井喷堵塞在件机overpressurization （讨论以较早者为准） 。