Is the nut tightened by hand?

The nut generally refers to the necessary items for fastening the screw. Although the screw and the nut are prefabricated, this is only for the convenience of threading and is also an important feature of fastening. Even if the strength of the hand is large, there is no wrench effort and a more secure fastening effect. The screw nut is pre-stressed to make it tightly coupled to prevent material stability from changing (such as thermal expansion and contraction) and loosening due to vibration. Spring washers are one of the most common  attachments. Apply pressure to the nut by applying pressure on the nut to prevent loosening. The premise is that the nut should be tightened with a wrench, and the strength of the hand is obviously not good. Some nut thread with nylon and other materials processing methods are also more common, using a hand to achieve a certain anti-loose effect, but the principle is to improve the friction between the screw nut. Plus a certain force tightening can further improve the stability, so even if you use the pliers during the safety period, it is more reliable than the hand.