The box of the chalk line is the part that holds the string line and chalk powder. There is typically a sliding door on the side of the box through which you can fill the box with chalk powder.
Door
The door is commonly found on the top or side of the box and usually has a small sliding panel which can be opened and closed.
String
The string or “string line” is the part of the chalk line that imparts the line of chalk onto the surface of the object. The string is coiled on an internal reel inside the box, and can be wound in via the crank.
The string used in chalk lines is typically thinner (2mm thickness) than regular string as this helps to make clean, crisp lines. Replacement strings are available.
Hook
At one end of the string is a small steel hook which is used to secure the string at the far side of the object or surface you want to impart a line on to. The hook has two claws which allow it to do this, as well as a tapered hole for hooking over nails and screws.
Reel
The reel (sometimes called the “spool”) is the part of the tool that the string line is wrapped around. It is similar to a fishing line reel and sits inside the box on a central axis.
Crank
The crank is essentially a lever that you rotate to wind in the string line. It is attached to the box via a pivot pin which allows it to be rotated around its central axis, which, in turn, rotates the internal reel and winds in the string. The crank can also be flipped over 180 degrees for ease of storage.