This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Screws are now used in building work to a much greater extent than was formerly the custom, largely on account of their decreased cost. They have the advantage over nails, as they do not split the wood, and they can be easily withdrawn when desired, without injuring the work materially. There are a great many different kinds of wood screws, which vary as to the shape of the head, the size of the shaft, and the length. They are made in about the same lengths as those given above for nails, and with both round and flat heads.