Ideal for including reinforcing steel bars
Tradies often refer to these blocks as being 400 x 200 x 200mm in size because the mortar width is also included in that measurement, and it is easier to work out bulk quantities required. The actual size is 390 long x 190 wide x 190mm high.
These blocks are open ended to allow for reinforcing steel rods (both vertical and horizontal) and core filling for added strength.