This section is from the book "Text-Book On Domestic Art", by Carrie Crane Ingalls. Also available from Amazon: Textbook On Domestic Art: With Illustrations And Drafts.
Ball and sockets are used to lap flat surfaces together, and are preferred by many to the hook and eyes. They are manufactured in four sizes and in colors black and white. They are more expensive than the hooks, and sold with a dozen on a card. As they are fitted on the piece of cardboard on which they are sold, so they must clasp together in the same way on the cloth. Some are made from a solid piece of tin, while others have a slit or a join. When the latter kind are used, never let the join come on the outer edge as it springs the socket out of shape. It is not necessary to space them as closely as hooks and eyes, an inch and a half or three quarters for the smallest size, and the larger ones near enough to prevent gaping. After marking the places they are to be attached, hold the socket part on the top or upper side with the center over the mark and fasten securely in each hole (there are generally 4 to each part). The part of the socket that shows is the wrong or under side. The ball piece fits in the center of the socket and may also be matched to it by placing a pin thru the hole in the socket having the lap of cloth in just the right position as when finished.