For hundreds of years, glue blocks have been used to reinforce woodworking joints. In recent years, they have gone out of style which frequently causes woodworkers to be called upon to repair loose joints. Sometimes when a joint loosens, due to other structural members that are attached to one or more sections of the joint, you can't pry it apart far enough to clean the joint and apply fresh glue. If the the pieces of the joint can be drawn tight, you can use glue blocks to repair them. Draw the carcass together and apply glue blocks to each corner with hide glue similar to what the original maker of the piece would have used.
Glue blocks are not only good at reinforcing joints in repair and restoration work, they are also very helpful in new projects. Glue blocks can be made out of 3/4" x 2" x the length of the hypotenuse strips. The ends are cut at 45°.