Why do some dominoes have a nail?

Back when dominoes were made of two materials that were pieced together to make a single tile or bone (yes, one of the material was usually bone) there needed to be a way to join these materials together so they did not just fall apart over time. Along came the small nail in the center.
    But now domino set with nails is also for the appearance of a design, Iraqi imports of domino sets are required with nails!
    Our factory can customise domino sets at wholesale prices and can customise many elements of the dominoes according to private requirements! Including the colour of the dominoes, the colour of the domino dots, the outer box and the size of the dominoes and so on!