Usually around 2 inches wide and of varied thickness. They are usually separated by a gap of around one-half inch.
Most plasterers feel that the uneveness of split lath gives a better key.
Lath should be nailed in its bottom half, because if it splits the nail will then support the larger part of it. Lath should always be soaked prior to plaster being applied. Reeds were often used instead of lath, and in many parts of the world, still are.