The holes are called ‘Core Holes’
Before ‘Core Holes’ were a thing most bricks has a large surface indentation called a ‘Frog’
So here are some reasons for the holes.
- Better locking in with the mortar. As the bricklayer taps the brick down the mortar squeezes into the holes improving the hold between the set mortar and the brick.
- Easier to Fire. When the brick is fired in a kiln the holes allow the heat to better penetrate the brick. . . . saves time and fuel.
- Lighter bricks. Easier on the bricklayer, and trucks can carry more saving material costs.
- Less material. More savings as it uses less clay