What is a Fastener for tools? a Fastener is a fixed or non-fixed mechanical tool that joins or affixes two surfaces or object together. As they are specialised tools, they are often manufactured in different shapes and sizes for the specific tools from common nails to heavy duty industrial equipment.  

Nuts are adapted with threaded holes that secure to bolts, screws and hold parts together.

Washers are thin plates with a hole in the middle (typically), that are used to distribute the load of a fastener such as a nut or bolt.