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.
As already explained, a splice is merely a joint between two pieces of timber which extend in the same direction, and is sometimes necessary because one long piece can not be conveniently or cheaply obtained. The only object in view, then, is to fasten the two pieces of timber together in such a way that the finished piece will be in all respects equivalent to a single unbroken piece, and will satisfy all of the requirements of the unbroken piece. This is really the only measure of the efficiency of a splice.
Fig. 50. Double Tenon Joint.
Fig. 51. Halved Joint.
Fig. 52. Dovetail Halved Joint.
There are three kinds of forces to which a piece may be subjected, namely: Compression, tension, and bending. A splice which would be very effective in a timber acted upon by one of these forces might be absolutely worthless in a piece which must resist one of the other forces. We have, therefore, three classes of splices, each designed to resist one of these three forces.