Basic Information
A bolt, in context, is a round of ammunition for a crossbow.
Similar to an arrow but shorter and broader to better adsorb the shock of firing the bolt is a less fragile, less refined missile but eminently suited to its role. Historically bolts were made of wood, metal tipped and flighted with feathers or strips of leather. Modern bolts may well be made of metal or carbon fibre and flighted with plastic. Specialised types of ammunition appear to have been rare and most bolts seem to have been standard 'general purpose' ones.
Bolts are also occasionally referred to as quarrells - although this term properly refers to the container in which they are stored (compare the quiver for the storage of arrows).
Assembly of bolts would probably have been carried out by an arrowsmith and/or a fletcher, but is unlikely to have been considered as high skilled as the assembly of arrows.