The handle of a brush is most often made from wood that’s painted and/or varnished, but it can also be made from plastic or bamboo. The length is variable, from really short (such as those in a travel paint boxes) to really long (ideal for big canvases). What’s more important than length is that the brush feels balanced in your hand. You’re going to be using it a lot, so it needs to be comfortable to hold.
The Ferrule, is the part that holds the handle and hairs together and in shape. It’s usually made from metal, but not exclusively. Mop brushes, for instance, can have a ferrule made of plastic and wire. A decent-quality ferrule won’t rust or come loose.
The bristles are the hair of the brush. Paint brushes are made from stiff or soft hairs, which can be either natural hairs or synthetic fibers. Soft brushes are ideal for thin paint which spreads easily, such as watercolor paint, and for detailed work as they can form a sharp point which allows for precision painting. Robust, hard brushes are ideal for pushing around thick paint, and for creating brush marks in the paint, such as when painting in oils using the impasto technique.
Crimp is the part of the ferrule that secures it to the handle.