Two types of proximity fuzes displayed

The video tutorial explains two main types of fuses: the ring type, like the T-90, and the bar type, like the T-51. Both types use the AN M103 fuse and operate similarly without batteries, being armed by a vein in the airstream. The primary difference is in their sensitivity zones. The tutorial also covers safety procedures, such as removing the nose plug and safety pin, and ensuring a tight fit with a lock washer.

What is the purpose of the AN M103 fuse mentioned in the text?

What steps must be taken to ensure the fuse is tight?